LOL!
My boy (an 'outie' when he wants EXCEPT overnight) has just passed his 16th Birthday.
I have had outdoor cats all my life, with ages ranging from 9 yrs - right up to 23 years!
The 9 yo lost due to spinal injury of unknown origin. Possible kick / car at 3 yo...?
The 23 yo lost due to a well-meaning neighbour taking him to the emergency vet when he went into her garden for some sun.
The vet decided to put him on a drip, and it did for him... he was on meds, which the drip counter-acted, causing heart failure.
The others as follows: one at 13 yo, one at 14 yo, two at 15 yo, and one at 18 yo....
I think it is largely down to breeding and how good the food and general care of the cat is - If you ignore illness / injury because of vet costs, then this will shorten the lifespan considerably, even if an apparent full recovery is made. Genetic or hereditary issues will impact, as will weight and nature. We had one obese cat, who barely ate any food, she had a stroke at 13 and passed a couple of months later. Her sister, who was always healthy, passed at 15, from cancer of the intestine.
It really is the luck of the draw, and if their number is up.... Merlin says I'm such a soft touch that when he goes, he's going to give Rainbow Bridge a miss, and is coming back to haunt me.... And I believe him!