Henry is some sort of houndy mix and I think he will live forever. He's 7 now and still whips the crap out of Rhys. He's not a high energy dog (mellowed out around a year old) but he's still very fit, agile, and active. His endurance is pretty awesome too. ***Knocks on wood*** he's healthy as a horse, too. Never had a major problem.
Rhys is an Amstaff and the age range for him is something like 12-16 years, which sounds about right to me. He comes from long lived dogs, and I think he had several great grandparents alive when his litter was whelped. Which is saying something since his mom was almost 6 when they were born. I know he had one great granddam pass recently a month shy of 16. His dad's dad is still very active and healthy at 10 or 11.
Many of the healthier APBTS/ASTs that I've seen age pretty gracefully and still have that terrier spunk into their teens. Cancer probably the most common killer, and many of the oldies suffer from arthritis, as was mentioned previously.