This is all pretty simple.
even if official explanation is diffrent, Attraction to any underage character is considered a crime by itself so it does not matter how old they are it is all about the fact that you like underage characters instead of mature women. the only reason why you are bot getting lynched is because there are some laws that prevent this just because of some side effect from other intentions.

also puberty is actually not underage. legally you can have sex with girls of age 16 (it is known as age of consent) or more at least on some countries, there is no need to wait for 18.

In the psychiatry pedophilia is attraction to the children below age of 13.

But in the moral terms this is actually not about underage characters but about characters that are subservient to you and do not have choice. as for example daughter cannot refuse her father or employee who dependents on that job cannot refuse boss.