We have been taught we "know neither the day nor the hour." So,
I think a good motto is to plan to live a long time, but then live each day as if it is your last.
In practice, I make plans for a long and healthy life and mostly act on those, but once in a while I stop and ask myself, if I only had one year left to live, what would I do? This exercise has led to a couple of radical changes in my life, and I have been pleased with the results.