You don't have to stop playing. Kasparov (59) still plays here and there and he's still pretty great. Anand is 52 and is 13th in the world.

Chess requires a crazy amount of time invested and you're likely going to stop, and definitely slow, making gains at a certain age. Lots of people play chess for reasons other than becoming the world champion (since obviously most won't).

That said I play online chess too much and it's sort of a waste of time ;)

Yeah, it's sad to see champions giving up chess in their 30s but I can also see the desire to leave on a high note, before you've declined, and also spend your life on other things- you've already shown you're the best so why invest all that time and effort into keeping your title? There's definitely diminishing returns.