I haven't been here in forever. How does this work? Some of them are adults but most are still babies even when I left. I just want to know the pet stuff. X.x

Hello! 
Pets will only age if they are on your profile

Pets on profiles will age naturally over time
every day their age goes up by one. 
At age 15 they'll turn into teenagers and at 30 they'll turn into adults. 

Mutants don;t have a teen stage. 

Hope this helps!