"In the long run"

Since my grandmothers lived to be 102 and 93, I fully expect to live a long life - in fact, I believe I will be 100. (The male side of my heritage is a little shakier, but there are extenuating circumstances. My Dad's father, a smoker, died of cancer at the age of 62; my Mom's father was killed in a car accident at age 38; and my Dad was 85 when he died after a long bout with Alzheimer's.) I amuse my kids by telling them that, despite this, I "only" plan to run till I'm 90, and then scale back to walking. But I am serious about this ... even though I'm sure I'll slow down considerably as I age, I intend to keep going. Should this work out, I estimate I'll have at least 25,000 - 30,000 miles ahead of me yet. (I just turned 52, which would mean 38 more years ... last year I ran almost 1200 miles, but don't know if it's realistic for me to keep up that average till the year 2047.)