5 years old is definitely not too late for a neuter, and it will definitely help with all of those pesky hormonal behaviors.

As long as your rabbit is healthy, 5yo is not too old to be neutered. It may take him longer than a young rabbit to recover from the procedure, just based on youth resilience perhaps, but many rabbits have been neutered within those ages and have lived long, healthy lives.

After a neuter, you may need to litter box train him so guide the behavior. Since he’s very used to pooping everywhere, the neuter may not miraculously make him go in just one spot on its own.

Do you have access to a rabbit vet who’s experienced in conducting neuters?

Again, sorry about the loss of your sweet Lola bun. Are there any rabbit rescues/shelters in your area that you could call? They usually know some good vets who they could refer you to.

5 is certainly not too old to get him neutered, if you are concerned about his health you can have pre-op bloodwork done to check the health of organ function before surgery. You could also come up with a list of questions for your vet such as what anesthetic they would be using and what sort of post-op care they recommend etc. Then you can check those answers before making a decision on whether to use them. Neutering will likely help some of those hormonal behaviours, and probably his litter habits too. Just keep in mind that sometimes a rabbit that has been doing those hormonal behaviours for years may not always stop them because they have also become habitual behaviours. So while he may get better at pooping in his litter box, he may not improve completely because he’s been pooping outside of it for such a long time. Hormones go away in a few months but learned behaviours are hard to unlearn. So there’s the possibility it may take a little longer.

Regarding your cat and the humping, it depends whether he’s humping primarily driven by hormones, or whether he’s humping your cat out of dominance. The humping will probably reduce, but don’t be surprised if he still humps your cat from time to time