It's generally a statistical trap to say that life expectency was in around 40s. From what I've heard, this number comes from the fact that very few children got to live long enough to become adults. But for those who survived past childhood - it wasn't uncommon to see people in their 70s.

And that applies all the way to ancient times. Remember Ötzi? He lived over 5000 years ago and died in his late 40s.