I actually believe what Canova said - 15 minutes. You tend to underestimate talent. Runnig is an ability but everybody naturaly acquires it. Sure there are stories of people running 25 minute 5k at a first attempt and then getting down to sub 15 or sub 14. But those must have been people who somehow managed to "conceal" their talent either by being unnaturally sedentary or overweight or unwilling to push and hurt a bit. I grew up in 80's so there were no computers then and TV content was crap (I am from Eastern Europe). I would spend hours walking around, playing soccer, hide&seek, climbing up the trees. I never ran more than 300-400m at one go. Sometimes we would chase somebody or were chased but as kids we would dash off hard and shortly after we had to stop because of being out of breath and feeling the lactic acid. Even when I rode a bike, 2-3 km on dirt roads felt a long distance. So I formally ran 0 miles and yet at school when we first ran 1500m at the age of 12 I won in 6:20, probably because I was scared by the distance, 4 laps seemed so long and did not go out too hard like the others. Next year I improved to 5:50 and then at 14 I ran 5:20, still 0 formal miles, just by the virtue of growing up and being physically stronger. After each race my calves were sore for several days because I was not trained to run that distance yet I ran a time that some healthy and not overweight your men will never run. While at I high school I became more sedentary, even more so later on, only playing soccer once a week. That went on until I started to run at the age of 35. I was 15 kilos overweight but shed them quickly and after 6 months running 20-30 km a week in my first 5000m race I ran sub 19 and 1500m in 4:50. A year later on 30-40 km per week I was at 4:30/1500m and 17:30. I got pretty serious about it for a few years, running some 80-100 km weeks but only improved to 4:15 and 16:30. Maybe if I trained more, smarter, harder and started sooner than at 35, I would run 4:00 and sub 15 but no amount of miles or the smartest coach would make me run substantiality faster. Based on the above, I estimate that my "untrained but not overweight" ability at the age of 25 would be 21:00 if paced properly. So how can somebody claim Bekele would run a similar time.
It is not popular to put talent first because it is something we inherit from parents rather than earn by hard work and the mantra over here is to run 100 miles a week year after year to gradually improve and let your dream come true because that is applicable for everyone while the odds are you are not the one with talent. How would Haile, Bekele, Wanjiru or Komen be world class runners at the age of 18 - 19 then?