Was the average adult life span in Regency England somewhere in the early 50s? I can't find this anywhere. It has to do with parent-grown child relationships in JA.

Assuming, for instance, that the Bennets had their first child when Mr. Bennet was 25 - that would make him 47 years old at the time P&P opens. Does JA mean us to understand that he is likely to die within a few years, thus placing much greater urgency on the need for one daughter to marry well? And at what time of their lives would Emma, Fanny, etc. have to think about caring full-time for an infirm parent? How would this affect their need to settle down with a supportive husband?