Many settlers became very ill their first summer, and this was called their “seasoning”. Colonists had not yet built up an immunity to diseases such as malaria, which were prevalent with the warm, moist climate, and many died. Other epidemics also periodically killed off some of the population at various times.
Even among the locals, a high percentage of children died young, and numerous adults didn't live to be very old either. Many were married multiple times during their lifetimes, as spouses died. There was a multitude of hardships and dangers in their primitive lifestyles that shortened their lives. Other than disease and starvation, there was the ever present danger of Indian raids since the colonists were infringing upon lands that the Indians had inhabited and hunted for many years.