Quote Originally Posted by Emerald Aeris
As for mentally, you can be very mature mentally for your age at 14 or 15, but you can't be mature. You can't be an adult until you are one. You can't have the wisdom that life gives you before you live it.
By which logic I can turn around and say you're not mature until you're 50 years old. Hell, my father was about as mature as a 12 year old. You say the law doesn't/can't work on a case-by-case basis, but in this situation it does, because we tend to be sensible enough not (As you pointed out) to go arresting 15 year olds for doing it. I'd also note that at almost every point in the legal process various people have various discretions, and that the law clearly does have a case-by-case aspect to it, but that's another discussion.

Generally, I don't think people 16 and under have the wisdom necessary to make good decisions in this area, and others (drinking, driving, voting, etc). Just because some people do sometimes, or some teens do all the time does not change that generally they don't. Laws should be in place to protect them from hurting themselves and others. Saying that some are mature enough is simply splitting hairs. It's irrelevant to the law.
Of course it isn't. The law's limits are placed at the point when it is decided that the majority of people are mature enough to handle whatever it is they're being allowed to do. The entire argument rests on at what age people are considered mature enough to not cause harm to others and themselves.

Edit: And it's ok to oppress a minority now?