Of the 3 requirements to get 100 pts (each) in the USMC "Physical Fitness Test" (PFT), the run poses the largest challenge for the average Marine. 18:00 = 100 pts, but it is not a "requirement". I think over 24:00 might have been a "Unsatisfacory" for youngest age bracket, can't remember, but there was a lower limit.
Many, if not most, would get 100 pts for the sit-ups during boot camp or OCS; many came close or achieved the 20 pull-ups, a strong kid can do with practice. As troops and officers get out to the "Fleet" and away from boot camp, the scores and maintained fitness levels go way down and the importance can get a little muddled until promotion time. My experience was that Officers (college) far outscored enlisted in the run.
In OCS, 18:00 was still pretty rare, MAYBE 10%, but I may be way off. By the time I got to the squadron, it was usually only myself and a couple running buddies of mine who would go sub 18. I always
scored "300" for every PFT, it was easy because I ran.
300 PFT in the Marines is considered impressive, especially as you age, but obviously if you are a for real runner, it is nothing. I was actually surprised at how few made it when I initially went to OCS, but the Marines are in general, a fit and exceptionally motivated population, but not necessarilly a group of super talented athletes, and it takes some athleticism to run or train to 5:59 pace.
My recollections include the crazy variety of PFT 3 mile courses, most were flat, paved, out-back runs which seemed about right distance. Some were way short, but what cracked me up is that all the different units would paint there own start/finish lines in different places on the road, obviously not trusting the other unit's measurement system or choice of starting line.