When did your child let you play with them?

At what age did your child begin to let you play with them in a fun, cooperative way?

My 2.5 year old always asks me to play with him, but then never lets me do anything. Sometimes I can do things, but only when he specifically tells me I can and even then it has to be exactly the way he wants it. I know this is normal. But when does it end? I would very much like to actually play with him sometimes.