What is the rationale behind defining child porn age The first case is something that actually happened to a friend of mine. He was 23 and dating a 17 year old, got convicted, sent to prison, and is now labeled a sex offender for life. Are there any countries out there that take a sane approach to this moral conundrum?
While the US doesn't ratify those conventions (because constitution) they do try to put them into law. That means they enact a mish-mash of bits and pieces, and leave out quite a lot.
England does a reasonable job here. We have the law (The Sexual Offences Act 2003 covers photographs of children), and we have prosecution advice (which covers things like whether it's in the "public interest" to prosecute.) The sexual offences act has some protections for people who are over 18 but who have a vulnerability impdeding choice (eg, a learning disability) or who are in a weird power dynamic (eg university lecturers).
There are also differences in law between someone under 13 (where it's assumed the alleged offender knew they were under age) and someone between 13 and 16/18 where the crown has to prove the alleged offender knew they were under age.
English law is a bit complicated because the age of consent for sexual activity is 16. It is weird that you can fuck a 17 year old, but you can't have naked photos of that same person. There's a narrow exemption in law for possessing images for people who are under 18 and married.
Here's the sexual offences act: https://www.legislation.gov.uk/ukpga/2003/42/contents
Here's the Crown Prosecution Service guidance: http://www.cps.gov.uk/legal/p_to_r/rape_and_sexual_offences/...