I'm a former D2 800/1500 guy. I wasn't great, but I was quite decent.
I graduated a few years ago and still run 2-3 days a week to stay in shape. Occasionally, the topic of running would come up in discussions with co-workers, such as during the 2012 and '16 Games. A few of them were bold enough to challenge me to a race and place bets. Easy money, I thought, but I couldn't have been more wrong. All races were done on a rubberized track without spikes and were hand-timed.
100m: The guy who raced me was in his mid 30s, about 5'10", and weighed at least 230 pounds. He asked for a 10 meter head start since he was 10 years older than me, which I agreed to without hesitation since he had a massive beer belly. But I almost regretted it, as he took off like a rocket despite all that weight. I barely caught up and passed him right before the finish. Times: 13.8 for me (110m), 13.9 for him (100m).
200m: This guy was about my age and not obese. However, he was a midget (5'4" with shoes, 5'3" without) with no athletic background besides a season of high school football. There were no head starts this time, and I was quite surprised at how fast those short legs spun. Times: 26.? for me, high 27s for him.
400m: This guy was a tall, lean dude who played ultimate frisbee and basketball a few times a week. He had no track background, but he ran and paced this race exceptionally well. He had the outside lane, and we ran the first 200 in 28 seconds or so. But instead of slowing down, he took a quick glance back, shifted into a different gear, and finished it in 55. I actually lost this race and finished a few strides behind him.
So there you have it. It may be a small sample size, but it clearly shows that the average guy can sprint much faster than many of us would expect. I think it's because our perspective is skewed - as distance runners, we mostly neglect our speed, so even a 65 second 400 seems quite fast. But it shouldn't be given proper training, and I have no doubt that most of us who can't break 60 in the 400 (but got close) would be able to break 55 if we did nothing but sprint training for a few months.