Total time means S.F.A. as far as flying ability goes.
Age will have an effect on ones motor skills eventually......when will vary from individual to individual.
Personally I decided to retire a few weeks before I turned 70, as far as I know I was still fairly competent in my airplane handling skills when I decided to retire.
I did do some flying for pay since I retired but have now decided not to renew my pilots license medical so I won't be tempted to fly for money again.
Soooo.....this winter I will finish my sail plane license in California and then do recreational aerobatics in sail planes.....that is a lot less physically challenging than flying powered aerobatic airplanes and I don't need a medical to fly one.
My message is we should know when to limit our flying activities as we age.
P.S..:::::
I still do a in depth medical every year and my last one a couple of months ago found only one issue....I was low on vitamin D....