And it won't hurt your horse to wait until age three. They develop mentally, too.
In fact, I have one colt that I didn't really get to as a three-year-old (had two other young ones, and ran out of time), so I'll start him as a four-year-old. I was feeling anxious about it, but he seems to be getting calmer as he gets older, so now I'm thinking it wasn't such a bad thing after all.
In the meantime, you can do some groundwork to get your horse ready.