Track and Field
The sport of Track and Field does not have the same kind of dividing line as other "Professional" sports.  It was only in the 1970's that elite athletes started to get paid for their performances.  Olympic medalists Bob Richards and Bruce Jenner cashed in after their competitive days by product endorsements.  Some senior athletes have managed to attain sponsorships simply for wearing a brand while competing.  Masters athletics is the division of the sport where athletes compete into, as mentioned, their hundreds.  I edited the separate section for Field Events out of this list, though if you wish to limit the Track and Field section to runners, there are documented cases of runners at age 101 or 102.  Everett Hossack, who was on Jay Leno's show at age 101, is the first name that comes to mind, though he might have been surpassed.