I would advise cross-checking everything your dad says with multiple sources online, because what he says is not true. Neutered rabbits do not have a shortened life-span, and neutering a male rabbit typically makes them much more happy day to day because they are not consistently frustrated by the need to mark territory, defend territory, and mate. Your dad would probably like a neutered male rabbit more because he would most likely be less destructive. Here are all different sources you can show your dad that can better inform both him and you about the benefits of neutering:
http://rabbit.org/faq-spaying-and-neutering/
http://articles.extension.org/pages/33105/spaying-and-neutering-your-rabbit
http://myhouserabbit.com/rabbit-health/spaying-or-neutering-your-pet-bunny/
http://rabbitresource.org/care-and-health/spay-neuter/why-should-i-spay-or-neuter/
http://rabbits.life/how-long-do-pet-rabbits-live/
— Getting another rabbit is also a big commitment, especially starting out. Both rabbits need to be fixed, at least 1 month needs to past after each surgery to their hormones can get situated. During that entire time, they CANNOT be together in the same area, or even areas directly next to each other because rabbits can mate and fight through bars. After both are fixed and a month passes, THEN you can begin to introduce for SHORT periods of time, eventually increasing over a period of months to them permanently being together. This is called rabbit bonding, and it’s a long process that requires a lot of space, patience, and attention. It can’t be done half-heartedly.
I recommend learning more about the best possible rabbit care for Jack, then after establishing he has the best quality life and set-up, discuss whether another rabbit may be an option.
Can you describe his lifestyle, environment, how often he sees you and others, diet, etc..? Also, has he seen a rabbit-vet before?
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.