when there is a high percentage chance of not making it home to your family at the end of the day. no matter the age!!!!
Grandpa shot his compound into his mid 70's, only things that changed were how far he would walk to sit a stand and his draw weight.
I am fairly below 55, but my hunting buddy is in his early 70's and he shoots a verticle bow and he is good with it! He climbs higher in his climber stand than I am willing to go and he seems to "see" more deer than I do and I know my vision is much sharper than his. Age is just a number..