wellll you can wait a little longer OR .. buy him some undies.. refuse to put him in diapers put him on the potty every 20 min or so.. get him a potty chart with stickers .. an give him a treat after he goes. buy him his own little potty so you can put it in the living room or any other room in the house an let him sit there whenever.. if he gets the runs NEVER put a diaper back on!! .. i made that mistake when my son was 21 months .. just for the weekend and it backfired i had to wait until now which he is 26 months and now fully potty trained.
I put a fruit loop in the potty for my boys and made a game of it. They thought it was fun to potty in their new potty chair. This even worked for my autistic son. Treats and special praise helped alot too.
There are some online books- potty training boot camp gives a pretty good overview of the common methods for pretty low cost. Oh yeah, make sure you have lots of patience =) I trained mine at 19 mo and 21 mo respectively. They both were fully trained (except for nights) and I mean down to maybe one accident a week, if that, by 25 months.
With a boy---and I had 3---you might want to wait til he is older----boys are harder than girls and generally not ready til older----this summer would be more appropriate and easier---shorts or just a pull up is easier to potty train in than long pants----and get his daddy involved in it.