"In ancient Greece pederasty was very common and quite fashionable"

We have an age, known as the age of consent, persons under that age are deemed not mature enough to have sexual intercourse. In Aciant Greece the age of consent was lower (12 I think, but don't quote me). therefore sex with a 12 year old was perfectly legal.
Under UK law a person still needs the permission of their parents to get married or live away from home at the age of 16 (the age of consent). By law they are still a child, therefore sex with them is probably definable as pederasty (although not illigal) and most people accept it.

This is a simple statement of facts (although possibly not very well explained) not a personal attack Ted, I'm pointing out a simple difference in values between two widly disperate cultures.