At certain age, if you yourself will know its time. Its not like other career that doesn't need agility of your youth. Your skills doesn't depend on how fast you chop the spices but how good the taste of the recipe.
For us speculators, it's easy to say that they should just retire. We can't feel their desire to continue.
I agree, for us it's easy to judge the boxers base on their performance and say that they should retire because they have been beaten very badly that they can't retire. But, the next day, those fighters will have a different mindset and want to comeback strong.
As for me, we should just let them do what they want. If at some point they experienced terrible losses and they feel their body is not cooperating now, they will retire right away without any hesitations. And even for let's say they want to continue, the promoters or organizers might not be interested now to form a fight and that will lead that old boxer to consider retiring and call it a career.
And so they will go on with their careers, not just for fighters that is about to retire, but again, as I have said, those who for example have been knockout or lost in the card and was dominated. And so they want to proved something to their fans and critics that they can still fight after this circumstances and will come back very strong and maybe avenge their defeat.
And that is the spirit of a true warrior because a warrior won't just give up after the loss he experienced, instead he takes that loss as to be more determined in the next fights and will be a reminder for him not to taste that bitter taste again. For Donaire, he believes that he can still make some diference in lower weight that's why he chose to not to retire. Let the man do what he wants, we will see it soon if his decisions will be worth it.