The rigor of Basketball is much more than any other professional game and should therefore have a retirement age 'cap' before 40. Ray Allen retired two years ago before he came out of it, and has now finally announced that he has fully retired.
In fact even one of the greatest players of the game, Michael Jordan, gave up at around the age of 40 after series of 'retirements' from around 32 years of age.
Just think, there's potential for even more improvement. Allen hasn't played in the NBA since the 2013-14 season, but he always left the possibility of a comeback open. Until now. From here on as a retired man, it's all golf, and the clock is ticking on qualifying for the senior tour.
I'm sure that running around almost every day has to have some sort of wear and tear on the body. And I'm sure it gets worse and worse over time. 40 is a respectable age to retire from professional sports. It's a very taxing job and you have to think about what's best for your health in the long run.
Ultimately, it is up to the player. If the player feels like they have nothing left to give, then they don't have to give anymore. Just because a player is 40+ years old does not mean they are ready to quit. If the players want to keep pushing, let them keep pushing.
This 2016 Free Agency was one of the most wild ones in the history of the league. There were over 3 BILLION DOLLARS spent over that time. If you were a free agent this year and were atleast O.K. You could literally get a 10 million dollar deal. Back then I'd say you should retire before 41, but now the money being given out to these sub par players is insane.
Ray Allen is one of the best three point shooters of all time and you don't need a lot of athleticism to get open for a three point shot. There's usually space to find and you aren't counted on to do much other than shoot three's. A lot of other players have had great careers into their 40s being three point specialists.