The older I get, the harder it is for me to find a good book, particularly those that are business or career related. At 56, most of the fitness books aren't right for me either. They are geared to a younger generation, who still have the stamina, energy and motivation to perform exercises that would put me into an emergency ward or traction.
Self help books are hard to find for midlife men. There seems to be plenty of books for midlife women to survive menopause, or the loss of their youth and looks.
Readers my age can find a large number of books that offer advice on retirement and financial management for senior citizens.
I think there is a market for books, particularly novels, to readers with some gray in their hair and a lot of candles on their birthday cakes.