It's a tricky one. In Britian we have one of the highest teenage pregancy rates in Europe partly because young people have having sex underage and haven't had the correct sex education up until that point.
The thing is, I don't think most controceptives are avalible to underage young people so that compounds the problem.
The reason why there's an age limit (did you know it used to be lower?) is because at such a young age there is a blured line between what is consent and what is not, especially when one party is older than the other. Legally a young person in Britian is still esentially a child at 16 (despite what bus tickets cost) and so it becomes not about maturity but about age. And sometimes, with relationships, those two things are the same thing. Maturity comes with age when relationships are involved.
You'll notice I'm avoiding giving a person opinion up until now but here it is. I don't think underage sex is a good thing. Not for the young people or anyone else. Setting aside adults or older than 16 year olds taking advantage of underage people I don't think that even two concenting 14 year olds should be having sex. (Also setting aside any Christian views I have as well).
At 14 I didn't have a sexual cell in my body (although my cells were reproducing asexually, sorry biology joke) and emotionally I would not have been ready. I over think things alot so I definately know what I'm emotionally capable of and that, at age 14, would not be something I could go through with.
Girls in particular are most at risk because to them the line between sex and love is blurred, for a girl sex is love but if they get sex before love that can damage any future relationships as they think that one will always equal the other and visa versa.
Anyway, there is so much more to life than having sex, young people seem to treat it like some sort of badge of honour. By the time people hit their 20s sex stops being such a big deal, I wish that message could get through to the poor young people who think that the only passage to adulthood is sex.