Let's also not forget that a 4:50 mile off of basketball training is not that exceptional. We had a sophmore come out from b-ball and run 4:48 at my high school. He ran between 4:50 and 5:00 regularly during pre-season training on a dirt track in training shoes. He ran with us in track and only got 2 seconds faster in the mile, he also ran 2:05 880.
Anyway, he will never know until he tries. Start building up the mileage and racing all distances to see if he likes it and improves. No matter what it will not happen overnight. Most people have run 4 years of track and XC by his age and most that run sub 2:20 run 4 more years of each in college.