Actually, there IS that much of a difference. Because the behaviors are diffferent. The pedo is attracted to kids who are not sexually self-aware (or sexually sentient). Once puberty hits, the pedo has no further interest and moves on. The OTHER behavior is the perversion of being attracted to dramatically younger but nonetheless sexually sentient partners - i.e., fully-developed but underaged teen girls.
What has caused the perversion in the language is the legislative insistence that every person even one day younger than 18 is a "child." This leads to situations where a nude photo of a girl aged 17 years 364 days is "child porn" and the same photo of the same girl taken 24 hours later is "legal erotica." Whenever arbitririness enters into the picture, lines of behavior get blurred and linguistic precision goes out the window.
Michael
That's a very good point, and its implications don't just stop on this subject.