How to cope with bursts of anxiety about one day losing my big dumb idiot

I adopted my 12M cat in 2020 at (allegedly) age 8. It was just recently both his gotcha day and his birthday, and it just hit me that he's really, truly getting to be old.

Adopting a pet comes with one day saying goodbye but after finding this sub and reading too many sad stories i'm nearly paralyzed with fear of loss. Ftr he's never had major internal health issues and is reasonably energetic. But what if it all falls apart suddenly, or he has some unknown issue i could have caught?

It's like confronting your own mortality except it's on behalf of a 12 pound baby man who doesnt know.

I have experienced the death of a pet, a childhood dog that passed away a few years ago. I do not know how I will feel about my cat. Anyone have any good ways to offset these kinds of scaries, especially not knowing what the future and old age holds?