When in sprinting shape, no specialized distance training outside of what he already does.
I'd say 4:50. Does two laps in 2:22, fades hard to a 81, closes in 67.
When I did some sprinting in middle school I ran the PE mile much faster than when doing nothing at all. And the amount of training that Olympic sprinters do all day really adds up. But I think you need to work on endurance to get into the 4:40s.