My mind is open, and I'm interested in what you have to say (that sounds a bit patronising but I enjoy your posts and my posts tend to come across as confrontational even though I am pefectly calm, so I thought I would just disclaim it quickly!)
Like I said, I teach these kids. In our system, secondary/high school starts around 12 and ends around 18. However, we also have a lot of kids who are held back, either in primary or secondary school. So a 12 year old and a 20 year old can end up eating in the same canteen. Moreover, I have a lot of groups where a 15 yr old and an 18 yr old are in the same class. They follow the same courses, have shared exam stress, live through the incredibly horrible experience of puberty together. And yes, there are differences, even in that same class group. But the connection they make, spending time together and getting to know each other, is often a lot stronger than the - often pretty shallow - age difference.
I also spend a lot of my time teaching (in one way or another) sex ed. I did two sex ed classes in second year this year (13 and 14 yr olds), where some of the kids had never dated or kissed anyone, and others clearly already had some sexual experience. I teach catholic religion in 3d, 4th, 5th and 6th grade, meaning I get them when they're around 14 or 15 and hand them over sometimes well after their 18th birthday. I see how they grow, how they change, and how they learn.
14 yr olds manipulate other 14 yr olds into doing things they don't really want to do. Part of my job is to teach them to respect their own boundaries and pace, and to learn to say no; but also to respect other people's boundaries and pace, and to learn to accept no. There are strong cultural differences surrounding that, and it's not an easy subject, but my students do talk about sex with a lot of insight, and they're eager to learn - how to say no, how to make it more enjoyable, why it's not always good, why some people wait and others fuck around. They're a generation for whom sex is omnipresent, and there's so much pressure on them to have it: it needs to be discussed properly.
But the age limit is thoroughly articificial, and sometimes it can do more harm than help. 14 yr old boys tend to be incredibly self-centered about sex, even when they really don't want to be. They tend to talk to older friends or brothers about it, often lacking experience themselves, instead of parents, or - even worse - look stuff up on the 'net. They tend to - involuntarily - make their first encounter unpleasent if their partner is also a virgin. The older a boy is, the less selfish he gets (whether he's a virgin or not). For a girl, speaking purely from a sexual angle, it can be a lot better to be with a boy who's a couple of years older, simply because at least they'll not board and retreat in under five minutes, and then be clueless as to what to do next. Older boys also tend to be more relaxed about sex, accepting their partner's wishes more, and not considering a rejection of sex as a slight against their percieved manhood.
I'm not saying this is absolutely true for everyone, but this is supported by litterature and research, and it's also really my experience from teaching teens and young adults for almost 9 years now.
Also, and this is a factor that's not often discussed: most gay teens have their first sexual encounter with someone older than them, because they're often a lot more insecure about what to do and where to go with their feelings and desires. It often requires someone who has a little more experience to set that in motion.
I think that as a society, we have this tendency to treat our teenagers as if they're children. The problem is: they're not. Yes, their brains haven't fully grown yet. All over the world, fourteen year olds get married, have jobs, fight wars. I'm not saying that's a particularly good or bad thing, it's just a part of life. We've gradually raised the moment of entry into adulthood from 12 to 18 and even 21, and it's creating all kinds of problems.
Yes, a lot of teens get pressured into sex, whether it's from an oversexualized media landscape or by a partner who threatens to leave them or expose them as a prude if they don't. But that partner doesn't have to be older, on the contrary.
I'm going to give one other example: one of my friends, also a teacher, had a student in 3d grade (she was 15) who had a crush on him. She would linger after class, ask him about his favourite movies, stand up for him when her classmates made it difficult for him to teach. He was about 24 at the time. Gradually, he fell in love with her. They started dating after she graduated, when she was 18. They've been together for three years now, and talking about marriage.
It's a relationship that has all the potential of being framed as a seedy predator/prey kind of thing. But I know these people, and it couldn't be further from the truth. Which is why I recoil when I see people described as predators simply because they're over an artificial, scientifically meaningless line in the sand.