T.C.
Every child is different. My oldest son who is now 3 1/2 went into a "big boy" bed at 20 months and NEVER had a problem with it. My youngest is almost 21 months old and she isn't even close. We know that with her it is going to be a battle keeping her IN the bed when it is time for her to sleep and she seems content in her crib so we have let her stay in it. I would say try it and see how it goes. If you have a convertible crib it's even more convenient because you don't have to go out and buy a new bed and you can go back to the crib easily if you have to. If you don't have a convertible crib you might want to just try a mattress on the floor for a few nights to see how it goes and see if he's ready before you go out and buy a new big boy bed.
GOOD LUCK
T.