No specific age, it just depends on how long I can be independent and take care of myself and that varies wildly from person to person.
There's a saying in medical circles, "If you've met one 80-year-old, you've met one 80-year-old". Some people are barely 60 and have all kinds of disabilities and health problems and have to be taken care of. Other people are perfectly capable of taking care of themselves until their 90s. It just depends.
I do have a lot of people in my fam that made it to their 90s (and my great grandma lived to be 100) so hopefully my chances are good, but who knows.