Here's a couple of examples of NFL Players excelly in the NFL at 40 Years of age.
http://www.nfl.com/player/tombrady/2504211/careerstats
2017 Season NFL MVP Tom Brady (Born: 8/3/1977)
Did you forget this Guy?
Brett Favre: Born: 10/10/1969
Brett Favre's Stat's 2009 included: 531 Passing attempts and 363 Competitions for a Career BEST 68.4 %
Favre passed for 4202 Yards that Season for a Career BEST 7.9 Yard Average.
He averaged 262.6 Yards/Game or the 3rd Best in his 20 Year NFL Career.
Favre had 33 TD's or Tied for 4th Best in his Career.