18 for a first 5k is definitely impressive but I wouldn't call it very talented compared to some people out there. I've seen numerous people run faster or equivalent+ times at other distances off no formal running training. If Salazar hadn't found Rupp until he was a HS senior and Rupp stayed healthy/stuck with soccer, Salazar still could've thrown him on the track and Rupp would be running mid-14s for 5k in a matter of months. Look at all te no name Kenyans like Dennis Kimetto who step on a course and run world class times superior to those ran by Americans who have been training since the 8th grade.
Also, "no training" is a very subjective term. I think it's retarded when people on this board try to define no training as having never competed in a sport, but personally I see it as simply having no experience officially training or competing in track/XC.