I've spent a lot of the past day thinking about demographics and how little I know about them. geesepalace observed that, contrary to my sarcasm, it's true that life expectancy in the Middle Ages was about 25. And he's right. If you don't take infant mortality into account, the number of children dying young brings the average age of death way down. (Although not as far down as it did late nineteenth-century Poplar, I'd bet.) Equally, however, it's disingenuous and misleading to do so. It gives the impression that the average person could expect to die in their 20s, which isn't really true. Anyone who survived their first few years in the period stood a good chance of living to 50+ years.
That's the standard line I've been using for as long as I've been having discussions about medieval life expectancy, but I couldn't tell you where the figures come from. What's the research on which it's based? Are they any better than the Black Death mortality rate estimates, which vary by at least 40% between the higher and lower estimates? Our statistics are only as good as our data, our use of them, and our intentions. The data's not great, but improving with every new census record and with many archeological digs.
So: medieval demographics. What are the major sources and who are the major authors? Joel Rosenthal has published several relevant articles and Old Age in Late Medieval England. I've found Josiah Russell's Medieval Demography: Essays. I'm intending to read Peter Biller's historiography work on the subject, The Measure of Multitude.
While, I'm asking, here's a related question from geesepalace:
On the other hand I've decided, based on no evidence whatsoever except my own retrospection, that most of the vikings and others who shared in what (I gather) was a sort of northern-european warrior death-cult were around 15 to 25. Not of course that they died out then, just that by their 30s fewer of them might have subscribed so whole-heartedly to the belief, unless of course they had risen to positions of power, where the cult would have served them well. For some reason contemporary artists who depict ravaging vikings rarely show them in their teens or early twenties. Do you know whether anyone's done much work on the age of the average viking thug?