I don’t think the 5 year cutting off of the lifespan is correct if you have a single male intact bunny. Like cats, intact male buns get into fights with other males and that can lead to very serious injuries and even death. Intact girls and boys can also fight. But fighting requires the presence of another rabbit.
Another thing that potentially could shorten an intact male rabbit’s life could be the stress from an intense urge to procreate. Before my Bam was neutered he had a crush on my dog, and I think it would’ve shortened his life if I hadn’t put an end to it by getting him neutered. He pursued the dog, circled her, peed on her, even nipped her. He’d follow her everywhere, all the time, and when I tried to separate him from her with a gate, he tried to jump the gate and bite his way through it. He was relentless, like a bun possessed. It must’ve been so stressful for him, and if it had been allowed to go on, I think he’d have had a heart attack or sth.
Male buns can be neutered when they’re old. My Bam was at least two, maybe older (he’s a found rabbit). If a bunny is on the old-ish side you can have blood tests done beforehand to find out if his liver function is good enough for him to cope with anesthesia.
Here’s an article about testicular cancer in rabbits. Richard Saunders who is listed as a contributor to the article is a very well-renowned British rabbit vet: http://www.vetstream.com/treat/lapis/freeform/testis-neoplasia-overview
(Neoplasia means abnormal growth of tissue that usually forms a mass, in which case it’s called a tumor.)