longevity

I would like to know how much long life in one or both parents can effect a child.  My father died at 70,but my mother is still going strong at 93.  If that is so much a factor how can people improve their longevity by exercising if the genes in the family say no.  I worry about my girlfriend whose mother died at 77 and father at 49.  Her grandmother died at 83.  Thanks, Maurice