In late August of 2015 and within sight of the summit hut, I turned my son around when his energy level and mood bottomed out and he complained about his chest hurting. We had spent the night at trail camp after a slow hike up to there, too. A tough call but, the right one.
In June of this year we set out from Horseshow Meadows on Father's Day morning and spent five nights working our way around to the tarns above Guitar Lake, four of which were above 10,000'. We summited on the 6th day and descended to trail camp for one last night. A huge difference that still could have been thwarted had it not been for a very nice lady with precisely the right snack right around our turnaround spot from the year before. Best advice I can give you--do not underestimate the difference between 13,000' and 14,000' (it is huge), and be sure to have adequate snacks--that your son wants, no matter how junky--for that last push. A healthy snack is useless if you cannot get it in the kid's belly.
I would be happy to share the details of what the challenges were along the way if you would like.
