Think of it this way: If it ain't broke, don't fix it! If the baby is happy in the crib, not jumping out of the crib, and not actively asking for a big boy bed, then don't move him until one of those two things happen. Some kids move earlier and some kids move later, but if you follow his lead you'll likely have better results and it'll be less of a 'novelty' (where he won't stay in his new big boy bed, despite all your efforts, and it becomes a total headache/nightmare for you).
Our son was 30 months (old!!) before he started climbing out of the crib. The next day, we converted it to the toddler bed and followed Weissbluth's techniques for the 'jack-in-the-box' kid who won't stay in bed. The first two nights were a little frustrating until we learned that he stays in bed for daddy but not for mommy. Now, a mere two weeks later, he goes down perfectly for bedtime and doesn't get out until the morning.