Good question.
I have two friends who drove RV's until their mid 80's. It seems that many in good health will be able to drive until age 80 to 85.
But what is good health? Let me suggest a few guidelines.
1. Vision correctable to 20/20.
2. Normal color perception.
3. Normal depth perception.
4. Daily physical exercise.
Even with those parameters, I suggest that at age 80+ you may want to drive only during daylight. Night vision and depth perception decline at senior ages.
Keep on traveling!