Why is age difference bad in adolescent relationships? (ex. 15 and 20, or 19 and 14)

Johan, I see what you meant. You're talking about life experience differences. Like you said, if there's a five year gap, one has more experience than the other. Thing is, that's not necessarily true, relevant or important in the least. At some point, it's more about what "clicks" than anything else. Not to mention, no matter how much or how little experience they've had, it's their first time with you.

Ideally it wouldn't matter that much but we live in a cruel world. Most adults want to take advantage of teenagers. There is a lot of development during those ages as well so teenagers tend to be easier to manipulate. It's really about protecting that development.