I'm not quite sure what you're saying by this. Who are you replying to? On the question of life expectancy I would say it was lower, but as pointed out infant mortality skews it. It also depends on class as poorer people were somewhat more subject to overwork, injury disease and famine. In relation to dropping dead at 40 the influence of disease on everyone as a major risk did make it more chaotic and frightening I think. And in a lot of the cases I know it comes off a bit like one's deal with the devil was run due, once they older they often start picking up ailments and it tends to snowball. The main character in WIP who was a real person died of a combination of scurvy, two tumours beneath his lungs and a small dropsy. Not fun.
It is just a common misconception. As early as Antiquity, if you survived first few years, you actually had a good chance of living until the age of 60 or so.
Regarding light, there is an interesting video on making rush lights in YouTube. Same guy also has a series of medieval life videos including some on food, clothing etc.
I'll be honest, this is pretty much my whole ethos for writing fantasy. Case in point! I will never let realism get in the way of cramming as many swords into the story as I possibly can!
