Will my dog live longer than expected?

I have a 5 yr old female English Mastiff. She is 90 lbs, avg weight for a female is 120 - 160. She is definitely a lot smaller than others of her breed. Does this increase her chances for a longer life expectancy? (Normal is 10 - 12 years). She's fairly healthy, and is the love of my daughter's life (also age 5, they're literally 2 weeks apart in age). Daisy is already getting a little gray, but she hasn't slowed down any, and all her check ups say she's very healthy. So... Any thoughts on if we might have her an extra couple of years?