My son has some crazy unnatural ability to adapt to altitude (maybe it is the Swiss ancestry on my side of the family 
) but he’s done plenty of easy runs at altitude (as high as 9000 ft) and even some (admittedly slow!) workouts when he’s been in Colorado, Utah, and Arizona over the last couple of years and it definitely helped his running when he came back to sea level. He hiked Hope Pass (12,600 ft) in Leadville with me when he was 11 with no issues whatsoever! It would definitely be an adjustment, but I think he knows what it would involve.
Yes, Denison is on the Ohio list (at least on my list if not yet on his!)! Thanks for the insight- that is really helpful!