Pet owners and farmers have known this since the beginning of time. But anyone advocating this form of mutilation for people is a monster.
If the man is old enough to benefit from this, he doesn't mind not having active sex anymore (passive is still an option for those so inclined), he wants to live absolutely as long as possible, he's of sound mind and able to make fully informed decisions, and it's fully voluntary with no coercion whatsoever involved, what, objectively, would be the problem?
What I would be uncomfortable with is this being advertised at any level. It shouldn't be pushed.