I honestly believe that kids should already be the age for the class before starting it. In child care they move up to the next age classroom when they have their birthday. In pre-school they have classes that are for the age group that is in for that school year. They have a curriculum that is for the age of the child within that year, for example, your child will be 2 years old and turning 3 sometime within that year. They would focus on that age level and the things kids that age are supposed to be learning and doing. That way they are in a class that is teaching on their level and things that are appropriate. No matter how smart or bright a child is they have natural developmental milestones that they work on in their age appropriate classrooms.
I think that as a 2 yr. old he would be best in a 2 yr. old classroom. He will NOT be in a school class that is not like this. He will have to be 5 before entering kindergarten...that's my point. He should be in a 2yr. old classroom if he is 2.