User blog comment:Emily Windsnap/How old are the Merlin characters?/@comment-96.232.203.146-20151109013257/@comment-97.125.97.169-20160208090034

This is actually a misconception. Life expectancy takes into account infant mortality, which in medieval times, was incredibly high. Survive childhood, and the next great killers are war and childbirth, depending on sex. Famine, disease... but a well fed person might easily live to their 70s or later. Average age of death in a culture means little on an individual level, as with all such things, the longer you live, the better your chances are of beating the odds. And age of marriage, etc. were not necessarily that young, especially in the nobility. Exceptions abounded, but truly, it was not that someone in their 40's would look like someone in their 70's if they were well enough nourished and had clean water and enough food. Life in the "underclasses" might be nasty, brutish and short.

I'd see Uther as 50-ish when the series starts, long enough to try for a son for years before resorting to extraordinary means.