Drugs. Lots of drugs...
That’s why his appearances are limited and sporadic. A heavy cocktail of drugs are administered to get him up for an event, and then a couple days are needed for his system to deal with side effects of being artificially pumped up.
Medication has side effects and everything goes through the liver to be filtered out. The older you get, the harder meds become on the body and the harder the liver has to work.
Ask Barry Bonds.