Totally agree with you on that. Hell, too many 25-year olds aren't even mature enough to be actual parents.
However, the problem of avoiding teenage pregnancy seems to be a rather different one than what we're discussing. I'd also say there's a far stretch between being mature enough for sex and mature enough for procreation. Aaaaaand of course, if you don't want the procreation, you'd better be ready to use pills, spermicide lube, condoms, backdoors, whatever keeps you safe. And we all know that especially hormone-ridden teenagers are the absolute masters of such careful planning!