My DD was 2 and talking her head off, nearly toilet trained and she was in a room with largely non verbal toddlers. I asked if she could go into the next room. I thought she would say no as the next room was mainly 4 and 5 year olds. (They didn't happen to have many three year olds). To my surprise, they readily agreed.
Problem!
From being pretty reliable with using the toilet, she kept having accidents. It was just really bad timing as she was consolidating her skills in this area and needed to be offered the toilet, taken to the toilet etc. In the older room, the children go to the toilet in pairs and are expected to be more independant.
So I felt a bit silly but i asked if she could go back down for a few weeks while she got confidence and independance with toileting, which she did, and then she went back up. She has just turned three and is the youngest in the room and she plays with 4 and 5 year olds. Our next problem is that next year some will go to school and she will not, and then the following year she STILL won't go, even though she is one of the most advanced in literacy and numeracy already. But so far, so good.
For the OP, having had a few childcare years under my belt now, I would not raise it now. I would start him and see how he goes. It totally depends on who is in the peer group, which you don't know and can't know yet. If he fits better into the next group they will move him up. If there is not a vacancy, they will wait till there is. No drama. Try it and see.
