Rashford was the fourth youngest player to reach 250 games for United and at 24 already has as many or more 50+ appearances seasons for United as the likes of Beckham, Giggs, Neville, etc. 111 matches and 7619 minutes over Solskjaer's two full seasons, while playing through injuries throughout that period.
If we're looking for a reason for him looking jaded now, that's it, not the charity work that keeps him occupied during his time off. He's been overpromoted and overplayed ever since he broke through. For his own sake and ours we need to stop relying on him so much.