I would say that they may have a slightly shorter life span than a cat that live in favorable surroundings their whole life. With a typical indoor cat, they are screened for illness more frequently and exposed much less in the way of infectious agents. However, I would expect the average feral cat to live within the range of 8-12 years (assuming no viral disease such as FELV, FIV, FIP, etc). Where I would expect the typical indoor only pet cat to live 10-14 in most cases. Obviously there are examples outside of those ranges, but I would describe those ranges as typical. I hope this helps and gives you direction.