My grandmother is still alive at 89 - though to hear her tell it, she's expecting to die any day now, what with the diabetes and her bad heart, and did I mention the broken hip that never did heal right? She even wrote her obituary already (she doesn't trust us to get it right). Although, she's been saying this for 15 years now, and I personally believe she'll be around for a while yet, by sheer force of will - as long as she has advice to give! She complains a lot, and she's pretty frail, but she also might be one of the strongest women I've ever met.
My husband's grandmother just turned 85 in November. She has a very active life in the retirement community she lives in - in fact, even though she is nearly completely blind now, she has a more active social life than I do. (I believe she and her friends are going to dinner and a concert next week!) She intends to be with us for a while, too - she wouldn't let us throw a big party for her birthday, because she was "only turning 85." The real celebration comes at 90, according to the custom in her social group right now.