Hi, fellow teacher :)
IMO, age won't be an issue if you're into a hobby. Even if you still playing LEGO bricks :D
If only there was one otaku teacher in my old school back then, then my school life would be more fun ^^ Thank god I had fun times when I was in teachers training college. It was during that time my passion for anime, manga & figures really blossomed.
Currently, only my family & a few close friends know I'm into this otaku stuff. But I did reveal my hobby to my ex-students when I had my practicum 2 years ago. It's good to know there are students who share the same hobby and it helps me to bond with them. But that was back then.
Now I have to test the water first. I think I'm the only serious otaku in my workplace...so far. And it's not fun at all T_T
Btw, this attracts my attention: "I don't like teachers who deliberately put a lot of time and energy into trying to stay young and cool." I understand that we need to connect with our students but trying hard not being ourselves is a no-no. Students know if you're genuine or not, am I right? ;)