I don't remember at what age I started. It just seemed to flow naturally. When he could hold a plate without dropping everything on the floor, I started having him clear his dishes from the table. When he started undressing himself, I made sure he put his clothes in the hamper instead of me doing it. When he started showing interest in feeding the dogs, I made it his "job."
Just look for readiness signs. Sam LOVES to have jobs. It makes him happy when he's able to contribute. (That is, most of the time!)
retsub:She's capable of putting her toys away, guess I could have her do that everynight...
that's a great place to start but do it as a relationship development not a chore... do it with her and make it a game letting her win. it won't be as much of a fight later on when she catches on. one of our parents was talking about how she just wants her son to pick up the toys without her since she does it faster. um, you can control how fast you pick up the toys. so, i told her to do it one for one at the begining but then after do one for his two and so on... it's worked so far.