Jack McClure is in his 80’s and literally drives the fastest kart around:
Once you’re in good shape physically and mentally you’re fine. There’s lots of more “seasoned” folks racing in the sport, certainly 60’s and 70’s. Especially if you look at vintage and road racing you’ll see a lot of these.
One thing I recall in the 90’s In europe, for an FIA license you had to do an annual EKG test once you were over a certain age.