Yeah, I'm also guessing he's around that age, maybe slightly older, like 21.

I don't believe his age has ever been specifically stated. I would assume he is at least 18, since he has lived on his own in the past. I've always thought he was somewhere between 18-22.

i think it was mentioned somewere that he's two years younger then Dick Grayson

In 2004 he was officially 19. Given slowed comic aging he should at least be 21-23.  However I heard that in the recent run of Doom patrol that they retconned his age by saying the year in which Steve and Rita adopted him was much more recent than it originally was.

So it's kinda up in the air until we get a new official statement in either the bok or an interview.

I always thought around 17/18.