The body starts to break down in all of us in the thirties. Most of us don’t need the extremely high function level of a professional athlete.
With normal levels of function one starts to run into limitations much later — 50’s and 60’s.
Golf is somewhat unique in sports in that the level of repeatable function from a static position is very high. Reflexes to react to a changing environment — think returning a tennis ball, hitting a ball etc — are not as critical.
In tigers case, the loss of mental focus — his fathers death and the dissolution of his marriage — is also a huge factor