M.S.
my advice is to let him go when he initiates it, but don't remind him, or make him go at regular intervals. make it something he has control over. if he goes in his diaper then runs to the potty, congratulate him, make a big deal out of it-- stickers, etc, because he is connecting the peeing with the potty... he's just a little late. i think he'll probably get faster and get it soon enough, especially if he's lucky enough to go IN the potty once or twice.
DON'T put him in underwear till his diaper's always dry. otherwise you'll be constantly worried about it, and you'll not be able to leave the house.
my son also started training early, but it became a real control battle becuase i was always forcing him to go when i knew he needed it but he just didn't want to..... kicking, screaming, wetting his pants......... it took a really long time for him to become independant about going, because i had taken him when i felt he needed to go, rather than trusting him to feel it.
i guess my point is that you want it to continue to be a happy thing that he wants to do, and not something that you make him do because you're worried about him wetting himself.