I was thinking about how impressive a sub-5 mile is for different age groups. In other words, as a male runner ages, at what point does sub-5 become impressive? (This is inspired by the 'what 5k time is respectable' thread.) By 'impressive' I mean more than respectable, as I think sub-5 is respectable for most people.
I would definitely be impressed by sub-5 at 50 years old. I think 45 years old would still be impressive. I'm not sure about 40 years old, though. What do you all think? Input from masters runners would be most appreciated.
On the other end of the spectrum, I'd say that sub-5 at 15 years old or younger is impressive as well.