Is There a Way to Figure Out a Cats Age?

Me and my husband got our cat about 2.5 years ago from the SPCA. We were told by different vets that he could be as young as 4 and as old as 10. Is there any possible way to really know?? The last vet he went to said he could be around 10. He has some gum line recession but his eyes are very clear and bright. He is not an energetic cat by any means but he still romps around the house a bit, especially when there is catnip to be had
He is absolutely precious to me and I would love to know an approximate age... I hope he's one of those freak cats that lives well into their 30's!!

I asked my vet this very question about our foster, Sassy (you can find a thread about her elsewhere).  She looked very old when we brought her home, but she's acting younger and younger. 

The vet said that there is no sure way to tell.
 

Very frustrating... well I just pray that I will have many more years with my Bo! Thanks again for your responses!