Being human, I think more about the number of dementia years than number of dementia-free years. Could having good dietary, sleep, and exercise habits result in living longer with dementia?

I've hard about cognitive reserve and how healthy lifestyle choices can build that. But I never read about ways to minimize the number of years you have to live with dementia. I wish I could sign an order that would grant me a dignified death once I'm deemed no longer fit to make that decision.