The secrets to Federers longevity in Tennis

Ideal body frame for tennis (i.e. 6ft 1) with wide shoulders for power and strong legs for a stable base and quickness. Players who are too tall are usually slower and are ungainly. Players who are too short have no reach and less leverage for power.

Although it doesn't look like it, have a really strong body core and strong legs

Little or no fat

I do not believe Federer does much gym work to develop muscles etc. or if he does he probably works on flexibility in conjunction with gym work

Relaxed grip and wrist for power and to allow a late hit.

Same ball toss for flat, slice and kick serves adds deception to serve. He still tends to favor the serve down the line for the deuce court and the wide serve to the ad court.

Late hitting adds deception to the shots. The wrist flick - most beginners to tennis get told that tennis strokes do not involve the wrist but that is wrong. The power in the forehand and backhand of Federer and most other pros is the pre-cocking of the wrist and the wrist snap that they make precisely as they hit the ball. It allows him to hit the ball even when out of position.

True confidence (or arrogance) that he can beat anyone.

the long hair..