It's Time!!! This is exactly what my daughter did, at exactly the same age. He's ready, trust me!!! If he dislikes having a wet/ppopy diapers, jump on the opportunity now before it passes by.
During the summer, I just let my kids (when they're potty training! LOL) go without underwear or bottoms when inside the house. Just get a potty for him and have him sit on it as much as possible. If you want, one day, pump him full of drinks and try to watch him like a hawk. When he finally goes on the potty, go nuts like it's a huge amazing party!! He'll catch on and want the praise.
When he finally goes to underpants, buy them a few sizes too big so that he can pull them up and down by himself.
And, pull-ups are NOT evil no matter what some people will say. The overuse of pull-ups is evil. I use them for night-time and naps so that my kids understand that "we're done with diapers forever." I think it sends a mixed signal if we expect them to potty, but then have them lie down to have a diaper put on at night time. Kinda defeats the whole "You're a big boy! You need to stop wearing diapers!" speech. Just My opinion.