A Facebook friend asked when and how I get my kids to clean the bathroom. I answered there, but I thought this might be a good place to put such information too.
It really depended on the child how early I started them. I think #7, at 2 1/2 can handle some of the jobs--mirror, walls, toilet paper. Others of my children I didn't start this young, though--maturity and communication level has a lot to do with it. #7's at the point where she's eager to help; though, I would definitely watch everything she does. I think the time to start is when they want to be in the middle of everything.
Definitely start young. Strike while the iron's hot.