Yeah I know this is a diet forum and all but don't look to diet alone for the extension of one's life and retention of one's abilities/health. There's a vid on youtube thats i'm having trouble finding, of this old chinese guy who does tai-chi on a daily basis. He's 116 in the video and still jogs like 5-10 miles a day. He wasn't on any special diet or anything (prolly cooked food, mostly veggies and grains) yet he was still was able to do everything he wanted.
Honestly I think there's the "energetic" aspect (still being researched) that alot of people ignore. For example TCM (traditional Chinese Medicine), Ayurveda, and alot of "instinctual" energy healers are known to work wonders for alot of people. Personally i dont really agree 100% with thier dietary practices but if you look into things like acupuncture, Qi-Gong, meditation, color therapy, sungazing, etc you can find many supplimentary practices that will also help extend the lifespan while retaining health. Actually I honestly think thats how the few healthy raw vegans that still exist do it. Storm Talifero is the only raw vegan i know who seems to remain healthy, however he practices tai-chi, yoga, tantra, etc which i think also nourish us on a diff level, but thats all irrelevant on a forum soley for diet...:p
And yeah like c_kid said you can look at yogis and such...actually the only one's who seems to thrive on plant food are these individuals(and others who do sum kind of spiritual practises)...but i have no idea how healthy they actually are, i just know that they can live for long periods of time.