Father Time is undefeated, no matter how great you are at anything. You can own the NFL with your skills and intelligence, but eventually those skills will start to erode, lost to the vagaries of age.
George Blanda played in the NFL and AFL from 1949 through 1975 as a quarterback and kicker, but time took him out. Jim Marshall played defensive end at a Hall of Fame level from 1960 through 1979 and never missed a game, but as sure as anything, the couch came calling.
The gift some players give us is the illusion of beating time.