In general they say kids are a little too young until age 2...like one mom posted, you want them to be able to be mature enough to actually comprehend what it means to stay there when asked and to stay safe in there room unsupervised (because they WILL get out at some point while you are still asleep). Of course every kid is different and it sounds like there are other moms on here that did it before age 2. I don't know how much difficulty it was for each of them during the transition and keeping them there, safely.
It might just be me, but I say if he is comfortable and sleeping wonderfully for you each night, then why mess with it???? You won't know if he is secure enough, emotionally ready or mature enough for 'rules' regarding the bed until you try and why open that can of worms when it could potentially be too early?? Maybe it's just me and I cherish the sleep I can get, but I would not want to welcome the problems that may come with transitioning too early (sleepness nights, crying out of insecurity, running around, safety while unsupervised loose in the room, etc). If he was giving you problems regarding the crib such as climbing out, getting stuck, etc I would do it now, but everything is happy, safe and content.... Many kids don't transition until 3....no rush!!!!!