Many cat owners think that once their cat has been diagnosed with diabetes, it will shorten their life significantly, but this isn't necessarily so.
If your cat was diagnosed quickly after symptoms were evident, and is being treated with the most appropriate type of insulin, plus, is being monitored closely by the vet with blood tests frequently, and checks on other major organs like the kidneys, thyroid and liver, keeping on top of things is essential.
If you feel your cat is not showing improvement, and/or is having trouble being stabilized on insulin, seek an opinion from another local vet or endocrine specialist, so you're assured your cat is receiving the best treatment and care.
Take a look at the following websites, which will provide you with a detailed look at diabetes in cats; also the feline diabetes message board (FDMB), I've found, is a very useful tool in helping cat parents with understanding feline diabetes and getting great advice from fellow diabetic cat owners.
Diet is also very important, and you can see more about the best diet for your cat here:
I hope all will be well, and please let me know if you have any additional questions. I too, have a diabetic cat who was diagnosed at the same age as your cat, and he's now 13 and doing well on PZI insulin.