I've always assumed if we are cloning humans for harvest and if you are cloning yourself that somehow your clone doesn't have to age the same way you did. But to the best of my knowledge you'd have to wait 18-25 years for adequate donor of your clone.
It's a weird thing. Hopefully we don't do this (Ala The Island) but can just repair replace lab grown organ or in place replacement.
I remember a story (but can't remember the name) where they cloned babies at birth so that they would have spare parts of the correct age.
But what if I'm born with a disease that ruin my kidneys by the time I'm 18? Both me and my clone will have that disease and will have ruined kidneys, so rendering him useless.
Everyone will have clones, simply borrow one from a friend's clone!