I don't think it's too early to start, although I'd definitely be making it a game and a fun thing to do together, rather than a chore.

The other thing to consider is putting at least some of the toys away for a time, so limiting the amount of mess that can be made at any one time, plus it retains novelty factor with the unseen toys when you do bring them out. I have about 3 "buckets" of stuff that I rotate around. I think that if there is too much choice, they end up being bored with it all, but if there's only a few things, then they actually have a better time playing with them, cos they're not overwhelmed with it all.