The 4-minute-mile is an average of 15mph. I haven't measured how fast I can sprint, but at my age (40s), I doubt its higher than 15mph for any timespan longer than a few seconds. So milers effectively sprint for 4 minutes straight. Its mind boggling what the human body can do.
I don't think you're familiar with the performance levels of masters (40+) atheletes.
I'm 60 now, but in my 40s I was a moderately good marathon-to-ultramarathon runner, and with a little bit of speedwork training, I managed to run a 5:30 track mile. That's not even fast - I had friends of the same age who could run 4:30.
It is truly remarkable what the human body can do - the world record for the marathon involves running 26.2 miles faster per mile than I could ever run 1 mile.
But if you can't sprint faster than 4mph for a few seconds, that's fine but it's not indicative of "at your age". Unless you have some actual health issue that prevents it, I would very surprised if you were incapable of hitting 6mph for a mile with some training, and a lot of people would not find it tremendously hard to hit 6.5-7mph if they had the time and motivation to train.
Not just that, but elite marathon performances (42.2 km) are under 5 minute miles.
Say, 2:10 (130 minutes) over 26.2 miles is a 4:58 mile pace.
The current world record seems to be 2:00:35, which is like a 4:36 mile pace.
Sometimes footage of elite level long distance running events shows fans trying to follow the runners on bicycle. It looks quite astonishing and ridiculous at the same time.
