There is nothing inherently wrong with consensual sex of any kind.
So, it comes down to defining consent.
First, in this context, consent means informed consent, not just being manipulated into saying "yes" or not voicing an objection. (I don't know how some people get consent from a banana or other inanimate object, but I trust their judgment. Farm animals are another issue.)
The important thing about sex is avoiding regrets. The ability to enter into an informed consensual relationship requires receiving and understanding information regarding:
1. How one's own body functions and how one's partner's body functions.
2. How to avoid an unwanted pregnancy or a disease that could make you sterile or kill you.
3. How to avoid future regrets about the encounter.
Even for those of you who actually had Sex Ed in school before the crazies took over, I'll bet you still don't know simple things like the fact that an aroused male, well prior to ejaculation, involuntarily produces a tiny amount of lubrication that can carry sperm, bacteria, and viruses. One is all it takes in each case, with just the tiniest amount splashing around. It is also possible to contract STDs and other bacteria and viruses from the natural involuntary discharge from nipples during sexual arousal, as well as bleeding gums, mouth sores, other open wounds, even tears, etc. People need to know these things, especially kids.
Abstinence-based "education" has been demonstrated to be idiotic. Against all kinds of sex, except between one man and one woman, of the same skin color, race, nationality, religion, and political and nutritional preferences, over 18 and married (yeess, to each other), in their own home, with the kids fast asleep, in their own bedroom, on their own bed, under the covers, with the lights out, in the missionary position, solely for the purpose of procreation (no condomsl), and for no longer than three minutes. And she better not have any of those disgusting orgasms. Remember, God is sitting right there watching and deciding whether or not this particular sex act pleases him enough to result in a holy pregnancy. And if our Republican brothers have their way, there will be a taxpayer-funded anti-choice enforcer sitting on God's lap right there in your bedroom watching you too.
Imposition of religion is an immoral act, particularly in place of science.
It is the failure of parents, schools, governments, and, in particular, the Republicans and their Christian Wrong base to ensure that young people receive the information they need and deserve. This failure fosters sexual transmission of diseases and accompanying sterility or death, unwanted pregnancies, unwanted children, and ruined lives. Legislation based on how a few nitwits think people should behave, instead of how they damned well know they will behave, is a crime against humanity.
Avoiding regrets is the hard one. It is very difficult for hormonally-enhanced young people to imagine, let alone seriously consider, that they (by that I mean "she") might come to view the encounter as something she might wish had first happened with someone else or not at all. The "popularity" that comes with sexual favors is not the kind of popularity you will wish you had later in your teen life - just the opposite. Best discussed with an older friend (as opposed to most parents). Forget the preachers -they operate on their own delusional, self-serving, witless agenda (more on that later).
Regarding age of consent, I know plenty of 50-year-olds who have no business making decisions about their own sex life, but you have to draw the line somewhere. Age of consent is 18 most places in the US (16 in Hawaii and Norway, used to be 12 in Illinois - we need to get our act together on this).
Then there is the issue that men and women are different (well duh!).
As with all organisms, our fundamental focus is on the perpetuation of our gene pool, otherwise our gene pool would have died out before we got here. (This is why the default initial reaction to the idea of gay sex is a quizzical look - by definition gay people contribute to the perpetuation of the gene pool indirectly. It takes an all-too-rare ability to think in more than one step at a time to recognize the value of having people around who automatically look at things differently from the humdrum rest of us.)
Humans being placental mammals, men and woman have fundamentally different views of sex. A man can potentially father thousands of children whereas a woman can bear relatively few, so the default male strategy for perpetuating his genes is to have sex as often as possible with as many women as possible including as many of the healthiest women as possible. A woman's strategy is to have sex with the healthiest male she can attract and keep to herself. Remember, we're talking about the last three million years, not just the last eye-blink in which technology has allowed social evolution to veer from its ancient course. People don't change, they just add on layers - those old ways of coping with life are still down there under all those layers of evo-talk from Cosmos. Recent social evolution has been comprised mostly of men conforming to the ancient women's strategy, but now that women are becoming more and more independent, for the many who have given up on finding a stable monogamous relationship, the pendulum is starting to swing back the other way entirely for both sexes. A stable partnership will remain the ideal for both sexes (after a certain age), but may remain unattainable for many, particularly those who cannot bring themselves to indulge in a little tongue-in-cheek roleplaying to keep the pressure off the ancient need to satisfy one's primal desires to dominate and be dominated. (The fundamental conflict for women - not wishing to be dominated, but wanting to be with the alpha male, which means the dominant male, which means being dominated, which means spending a lot of her time rebelling against it, which means every issue in the relationship bears the baggage.)
But, I digress. Well, maybe not so much. There still is the issue of age differences.
For adults with significant age differences, best of luck to you.
Regarding sex between adults and minors, a good example would be teacher-student sex.
There is nothing more both tragic and yet comedic than some news story about an attractive female teacher getting into trouble for having sex with a male student.
It is possible, even probable, that any human female might, in an instant, before, during, recently after, or decades after an anticipated, occurring, recent, or historical sexual encounter, previously perceived as positive, suddenly come to feel exploited, abused, or otherwise regretful, even if, or perhaps especially if, she initiated the encounter herself. Therefore, except in cases where a student's mature, informed consent can be reasonably demonstrated, male teachers who have sex with a minor female student should be candidates for prosecution. Same applies to male teachers who have sex with a homosexual or effeminate male student, since these students' feelings tend to follow the same trends as those of females.
In the case of a female teacher having sex with a minor male student, there are two scenarios.
First, if the student's participation was demonstrably coerced, through use of the teacher's authority or other means, then the teacher should be a candidate for prosecution. This would apply in .000000000001% of the cases.
In the other 99.999999999999% of the cases, the male student's feelings about the encounter, before, during, recently after, decades after, on his death bed with his last fond nostalgic smile, will be Oh Yeah! with a big thumbs up! His friends, father, other male relatives, future college buddies, future armed-service buddies, future co-workers, heck every guy he ever meets, will all feel the same way. The only people who will ever have negative feelings about it will be the bozo busybody perverts who are obsessed with what other people do with their own bodies, and, maybe, his mother. Prosecuting the teacher is idiotic. The busybodies need to learn, and the law needs to recognize, that yes, duh!, boys and girls are different.
That's right; the sex-repressing, anti-LGBT wackos are the real perverts, because, as I said, they are obsessed with what other people do with their own bodies, which is simply none of their damned business!
Regarding getting advice about sex (or anything else) from people who are mentally defective by definition, such as the aforementioned preachers:
Religion is perpetuated by charlatans and well-meaning fools. The oldest way to keep the sheep in line to make them feel invested in their religion so that they feel entitled to its "promises" and fear that straying will make all their prior investment worthless. The simplest way to make people feel invested in their religion is to make them give up some natural joy, such as sex just for the fun of it, and, of course, their money. People who make such foolish sacrifices get really upset with any suggestion that they have been duped and that it has been all for naught. To them, God owes them for giving up sex for the fun of it, not to mention all that money, and they are entitled to eternal life and bliss. They perceive any suggestion that they are nuts as a grave threat to their desperate delusions, and can react to contradiction in dangerous ways.
Anyone can be good without God.
Anyone who tries to do the right thing already has all the religion he or she needs.
The purpose of Life is Life, to get the most out of Life, to enhance the experience of Life for all Life.
If you appreciate the potential of the Greater Good, ask for ideas instead of "answers", and take responsibility for your own answers, you will be fine.
And, by the way,
nothing inside a woman's body is anyone's business but her own!
How foolish can the religious get with their obsessions about what people wear or do in private? What mature people do in private is simply no one else's business. A mature person is one who has been taught how, and is able, to avoid the common regrets: unwanted pregnancy, disease, traumatization of the vulnerable, sharing intimacies that one might later wish to have reserved for a soul mate. Beyond this, sex is just nature's way of reminding us that we are just pretentious animals. Are the politicians so foolish as to think we really need a marriage protection amendment? Sadly, it is certainly possible that they really are that foolish, but it is also likely they just need a distraction from their other failures, most notably, "abstinence only" policies.
I have never experienced an abusive relationship, but I have friends that have, and the big questions are: Why do people seek out abusive relationships, and why do they stay in them?
It would seem that abused people would be driven to break the cycles of abuse, but there are deep-seated factors that keep them trapped.
First, we don't change, we just add mental layers over our past experiences and predilections. Inside each of us lives all the previous versions of our personalities, who still perceive and react to life the way they always have, even though our conscious and outward selves primarily reflect only our most recently developed perceptions and reactions. Living inside every person who experienced abuse in the past is the younger self that still fervently wants and needs to believe that:
o The abuse never happened
o The abuse was not as bad as it seemed
o The abuser will say they are sorry
o The abuser will make it as if it never happened
When the abuser is no longer in the victim's life, the victim seeks out a surrogate in the subconscious hope that the surrogate will provide these reliefs. Without knowing why, compounded by fear of retribution if they leave, the victim's only way out is through outside help and intervention.