Looking at a sample of 40,139 death records from the Veterinary Medical Database from 1984-2004, scientists from the University of Georgia determined the average age at death for dogs that had not been spayed or neutered was 7.9 years versus 9.4 years for sterilized dogs.

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?

    There are those who are born UNIX;
    Those who are made UNIX;
    And those who become UNIX for the kingdom of heaven's sake.
    - Matthew 19:12