“Here, son! Play with these dolls ACTION FIGURES of scantily-clad muscle men in loincloths! That oughtta keep you hetero!” 
“Here, son! Play with these dolls ACTION FIGURES of scantily-clad muscle men in loincloths! That oughtta keep you hetero!”
We’re told they’re teenagers, but are we told specifically what ages?
I’ve never watched the shows or the movies but they’re marketed at young children, so I guess they’re probably young.
Apparently they’re roughly 15…
Boyhugging with a backpat and a “proud 'a you, son”
Yeah, in the 1980s series, they’re canonically all 15. It was printed on the toy packaging and in the mini-comics that they had back in the day.
You can probably pull the “wull ackshually a 15 year old turtle is like a 1,000 year old dragon” card here, and then we can
you for entertainment purposes.