Honestly, I don't really set an age limit. I won't judge people who are out for fun. I've been there, there's not much to do around where I live.
That being said though... Regardless of your age, if you costume up, you're likely to get more candy from me. (I'll also offer candy to parents and older siblings who aren't taking part because I'm cool like that. Just don't stick chocolate bars in your pockets LMAO)