Around 75 and just over seems to be the normal lifespan of the villagers with all the tech levels, just as it is in real life (in the developed world, anyway). A few will probably live longer, again just as in RL.
my population went up twice to two different couple but no baby
Sorry, I don't understand what you mean here. How do you know the baby was these particular villagers', perhaps another mother had a baby just at that moment? Does the fact that she is nursing appear in the mother's details?
Don't forget the action line changes as soon as a villager
decides on a course of action. The mother may have decided to wash her baby, but not have started off to the stream yet. You'll often see these seemingly contradictory actions, such as farmers who have given up fishing in the ocean and decided to enjoy the pond instead showing the "enjoying the pond" line while they are still swimming to the ocean shore. Barbara can give a better answer than I can, but I doubt this has any connection with having to reinstall.