Process of living is to be conceieved, born, grow, mature, get past maturity, decline, and die.
Decline is in the physical. Your mental works for another 30 years, so use it, compensate, adjust, to your declining years, which for most, starts around 35.
So, at 64, you play old fart's tennis. So what? You ARE an old fart.
That's life, you can't fake it.
Injuries are a part of life, and what separates you from IvanLendl. Accept it, you have no choice.