I started transitioning my daughter at 18 months (due to family pressure) and I regret it to this day. She was NOT ready and it was a very, very long and tiring process. She is 4 now and sleeps very, very well in her own room (she had absolutely no problem what so ever when we moved either which I just found to so shocking and amazing since I heard that children don't usually take to a move so easily). She was doing fairly well by about 3 and has really flourished since we moved to our new house this spring.
There is no reason that you can't start offering him his own room. Put a bed/mattress in the room big enough for you to lay with him. Then you can start a bed time routine that begins in his bedroom. We chose to have stories first and then we would snuggle and I would sing her to sleep. At some point in the middle of the night she would make her way back to out bed. After a while we wanted to encourage her to stay in her own room so instead of letting her crawl in bed with us we crawled in bed with her. Once she was back to sleep I (or DH, who ever had gone in with her) would come back to the big bed. Some times we would do this a couple times a night and sometimes it would only take one time. Now, she prefers her own room. If you're little one isn't ready you'll learn it pretty quickly. He may just surprise you though and take to it right away. Good luck! I hope this helps.