I'm 42 and have a 44 mi RT commute. I only do it 3 days a week because I have two worksites, and the second one is 64 miles from home. I'm in decent shape, but I encounter plenty of guys who are both older and stronger than me.

I don't encounter many cyclists on the roads, but when I do, they inevitably tend to be in the 40+ range, so I think what you're thinking of is doable. I'm not sure I'd want to do 40mi each way every day. I love cycling, but that would just take too long. Given a 40 mile one way commute, I'd probably ride 2 or 3 times a week if roads were decent. It would take discipline in the winter time. Regularly slogging that far in storms would be character building.