40 is past prime
I watch a lot of fight sports and it always seems 40 is the age where you are no longer in your prime. You'll see many people fighting good at 37 or 38 but it always seems like 40 is that magic number where over night they move like they need WD40.
Some people can last to 43 but 40 is around the time that its all over if youre in fight sports.