My old Fella (83) was diagnosed with Dementia back in June of this year. I had noticed a deteriation in his demeaner and he was getting aggy with people because he noticed that he was making strange choices and generally having no energy. Since his diagnosis he has been put on medication (can't remember what it's called) but it has turned his life around, even in such a short space of time. I would say it has taken 10 years off him in the sense that he has got his mojo back and is able to remember most day to day stuff. He has his moments but he is so much better.
I know it's only a plaster, but I'm glad that it's working for him, it doesn't always work for everyone apparently, maybe we caught it early, I don't know.
Keeping busy, getting out, Reading are all things that help keep dementia at bay.
One of the big factors is catching it early.