This A-Z, I’m looking at aspects of the Middle Ages that are relevant for writers. Old Age is an important one here, because it’s easy to forget that life expectancy was much lower then. Exactly how much lower probably varies by time and location, and in any case the lack of consistent public records means that it’s impossible to be accurate about, but we can make some general points.
First, there was very high infant mortality. There was also a higher than now risk to women in childbirth. There were the additional factors of common violence and disease. The end result was that even for those nobles we know about, making it to fifty (only three countries in the world today have life expectancies lower than that) was not common. Peasants would probably have had even lower life expectancies.
Yet there were older people than that. People could occasionally survive well into their seventies or eighties, typically within monastic institutions or royal houses. What does this mean for your writing? For one thing, it means that YA characters will find themselves pushed into adult roles and that will be normal. For another, it means that the contrast with the long lived creatures of fantasy will be all the greater. And those few wizards with long white beards who have clearly been around for longer than anyone else alive? Well, if you’re authentically medieval, that might only be sixty or seventy years.