They are teens but this show is so much more mature, so baffling the reboot went with the sanitized direction it did and it's such a slamdunk to like take the teen angst and replace it with young adult anxieties but TTL didn't even try to attempt that it's crazy.
I've gone through some TTA episodes and I can already say it understood depicting adolescence, coming of age dynamics better than the reboot because like the toons here are written like real teenagers there rebellious, hormonal, messy refreshing to TTL's squeaky cleanness lol