It does seem odd that family members live only up to 60 or so. You'd think that they'd live longer than villagers, not shorter, since they have access to modern medicine and so on.

The only reason I can think of is that it can get a little boring when there are just two old people shuffling slowly about the house; with the children gone off to college and careers perhaps mastered there's not much going on. Arthur may feel that it would improve game play to make that period relatively short.