Well... maybe it should be 13 provided the other partner is no more than say... 3 years older. And then 16 provided the partner is no more that 5 or 6 years older? I have no problem (or very little) with teenagers having sex with other teenagers.
It really doesn't sit well with me that it's perfectly legal for a 50 year old to have sex with a 16 year old who's still at school (or not) though. I remember the Sun used to have Sam Fox on page three just after her 16th birthday, yuk! And they had a count down to Charlotte Church's 16th birthday.