Yes, yes it could be used for that. Anything else would mean having to figure out if being a teenage means in human years or turtle years? And can one fully call it sex and not just another form of showing dominant over each other? And last seeing how they are in death dealing training and fights, would it just be a form of relieving some pressure in the form of sex?
They seem to be portrayed as to at least act pretty immature and teeny bopper as far as I can tell. So...I dunno. Maybe they're just retarded adults then? XD
Technically, eighTEEN and nineTEEN are still "teen" ages. But since they don't appear to be younger than adults IMO (except the 80's cartoon one, which makes them look like children), I'm more disturbed by the fact that it's technically incestual (despite how they may not actually be related, though unlikely that is).
https://www.youtube.com/watch?v=ojWHllijiAw