I remember hearing at one time statistics of cat lifespans. IIRC, it was 10 years for an indoor cat, 4 years for an outdoor cat, due to traffic, stray dogs, and diseases.
Our cats are allowed into the orchard garden, which is about 4 meters by 4 meters and 1 meter above ground level. There is a forest of shrubs in there, plus 4 coconut trees with metal bands (to keep out the rats which live in the trees), so it's a kitty playground. It's fenced with fishnet, so I foolishly thought the kittens couldn't get out. One kitten came bounding down the steps into the orchard garden just as JJ came out of her room. She made kissing sounds, the kitten raced over and up the fishnet, doing a flip at the top. She caught him as he plummeted. --I need a new plan.