Our office is pretty close to a track, so we decided to race a mile yesterday on a whim to "fight the holiday weight gain". About 70% of the office participated since the winner would receive $20. There was an "under 40" division and a "40+ year old" division for men and women.
In the men's under 40 division, the winning time was a 5:18, the median time was around 6:15-6:20, and the absolute slowest was 7:24 by a 225 lb guy in his mid 30s. The men's 40+ division and the women's under 40 division was about 1-2 minutes slower. I ran a 5:44 (still recovering from an injury) in the men's under 40 division, which was only good enough for 5th place.
Everyone always assumes that the average guy is out of shape, but that isn't the case. Not many people ran, but almost all of them were active in some way. Activities included triathlons, pick up basketball, soccer matches with friends, adult softball leagues, 10+ mile hikes, etc. Even the ones who didn't go out or play a sport ran on the treadmill quite frequently (150 minutes a week, so 18 MPW at 8:20 min/mile pace). The 225 lb guy may have been classified as obese based on BMI, but he was a muscle bound avid lifter.
Don't underestimate the average guy in their current condition. The person walking down the street may be much faster than you think.