Happy for the man, but only if he's serious about the retirement this time, 36 is still a bit young to be honest, and expected to still be able to handle alot of heavyweight stuffs, but also on the other hand, some factors have to be considered as well, like from what age he starting his career in boxing, this factor can determine if he still by now, would have the strength to keep it going.
But then, he owns his body and possibly knows the changes that has happened, if he feels less strength and powerful like he used to, instead of collapsing or getting killed in the ring, better to retire early, stay alive and enjoy the wealth he has amassed for himself and loved ones.
I would say a big congratulations to him, again, only if he is serious about the retirement though.