It's more complicated than this,
longevity (which is the concept you're looking for) was indeed higher than 40 years, but at the same time mortality all along life was still much higher than today and most people died before old age (men more so than women though).
But that's why I added the second sentence: from an evolutionary perspective it actually doesn't matter if you die from cancer at 60 when you're close to being great-grand father, you've done your job of reproducing and raising your kids well enough and as such it's a good time to go.
People often don't get this, but from a biological perspective death is not actually a bad thing, the only thing that matters is that you leave descendants bearing your genes behind you.