A.R.
Both my sons moved into twin beds by 2 years. Not a single problem. At first they were so excited that they jumped around but that night they slept great! It's a shock when they greet you in the morning though! I think starting with naps sounds great...I will have to move my youngest into a bed when he is less than a year and a half. I've heard that you should do it a little bit before the baby comes so the little one doesn't feel as though they are getting moved aside for the baby.