I think that that depends quite a deal on the Cats genes.
Pouncer passed on early at nine.Partly due to the fact that I gave her too much Human Food.
Mr Scrappy went at 15,Smokey was 23,Smoke was 14.
Munchkin sadly went at three.
BJ passed on at 10.
It depends on the food and care they recieve,but with the Food that they have now Your Indoor Cat should be able to reach 15 or 16.