If you think age is any barrier to mating in the chinchilla world, take 3 1/2 year old Maureen and 6 month old Max. Maureen had been with another male for a year and had never been pregnant. I knew the other male was fertile, so I assumed that Maureen was barren, but decided to get Max neutered just in case. In the meantime, I caged them together for a month. 3 1/2 months later, I found a little surprise baby. Thankfully, it was Max who was younger, so the pregnancy posed no risk to Maureen's health.
One option that you could explore is neutering Simba. I have had both Max and his son neutered with great success. However, Jade had a very bad experience with her male Elvis when the vet lied about his qualifications and botched the surgery completely. If you can find an exotics vet in your area who performs chin neuters and can give you references from amongst his actual patients, the procedure takes about 15 minutes and usually goes well. The biggest risk in a properly done neuter is the general anestesia in a small animal.
Lots to think about. Older males are a little harder to find friends for. They tend to be bachelors stuck in their ways.