Allow me to cheat by introducing some actual data:
http://usgovinfo.about.com/gi/o.htm?zi=1/XJ&zTi=1&sdn=usgovinfo&cdn=newsissues&tm=9&f=00&su=p284.13.342.ip_&tt=2&bt=1&bts=1&zu=http%3A//www.cdc.gov/nchs/data/ad/ad347.pdf
1) I'll assume that the "population" this thread refers to is the USA.
2) Because the data are separated into 20-29 and 30-39 age groups, I'll split the difference between the means of the two, in order to get approximate data for 30-year-olds.
3) I'll use data from the 1999-2002 survey of males. Does anyone think that American males aged 20-39 have gotten *thinner* on average since then?
Yeah, me neither.
4) I acknowledge that I'll be talking about the means for height and weight and the median for mile time. (Others have pointed out why we have to use median for the time.) This is not really an apples-and-oranges comparison, though; at worst, it's lemons-and-oranges.
Here we go:
Average height for American 30-year-old men: 69.6 inches.
Average weight for American 30-year-old men: 186.3 pounds.
Okay, think about that: this average guy we're talking about (call him "X") is roughly 5' 9 1/2" and over 185 pounds. (And that weight is not muscle.) His BMI is just over 27, putting him well into the "overweight" category.
Now: having taught adult fitness classes for a couple decades (in addition to having coached for a quarter-century), I can *promise* you that X cannot run a mile, period. That is, the percentage of American guys at this age who can run an entire mile is considerably less than 50; therefore X is running only part of the mile, at best.
Now the question is: How fast can this guy walk-and-jog a mile? Again, from experience I know that his time will be something over 12 minutes. (You don't appreciate how out of shape X is. He can't run for a minute at a time without getting seriously out of breath.)
[In other words: at more than twice his age, and having had a heart attack about a year back, I can *walk* five miles at about the same pace this guy can reach for a single all-out mile.]
The thing is, LRCers mostly are (or at least were) runners. They mostly are, or will be, college graduates. They mostly come from above-middle-class family backgrounds. (Everyone saw that I used "mostly" in there, right?) So they really don't have a feel for who X is, or his living circumstances.
X is not and has never been a regular runner. He does not have your education. He does not have your likely income (okay, maybe your likely *future* income). He does not have the orientation to physical activity that you, and most of the people you encounter, do. X might occasionally play a game or something, but he does *no* vigorous exercise on a regular basis. (He probably does some walking, but at a low intensity:
http://www.cbsnews.com/news/cdc-80-percent-of-american-adults-dont-get-recommended-exercise/
)
So you're asking X to cover a mile. He CAN do that, but he won't be happy, and his time--just a guess here, but an educated guess--is something like 13 minutes. Or a bit slower. All out.