I don't know if my DD is unusual but she started CC at 12 months as I was going back to work. She was obviously socialising with other children and playing with them from about 18 months. The carers acknowledged that it was younger than they usually see but they were very clear that she was definitely playing WITH the children and had a clear preference for her particular friends.

Now, at 2.5 she and her friends do socialise and play together - I have seen them pretend to make cakes and tea together and sit down at the table with each other and have a conversation. They also play games where they need to take turns and help each other. One day when the boys took her friend's doll from her DD went to the boys and said "No, That is Amber's doll, please give it back" and she got it and took it back to Amber.

Someone correct me if I'm wrong but I believe these are definitely socialising behaviours so I don't think that 3 years holds true for all children. I think you need to look at your own child and determine where they are at socially and make your decision based on the individual, not on what the "accepted" age that is touted happens to be.