If you have 40y life left but are mentally at half your peak acuity of 20s say, and also have half the stamina of youth (4h days instead of 8h holding intensity constant), you really only have 10y of 20s-equivalent life left at most, unless you do something differently.
Replying to @gdsimms
That's certainly the line we sell to the kids 
2:55 PM - 11 Dec 2017
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