To be fair, young players of exceptional talent are supposed to get given more leeway, and if he's a young player who is, going by (all pre-United talk) reports...
- The best rated player in all four matches he's played in, including when he came on as a substitute
- Scored in three of the four matches and got an assist in the fourth.
- Considered to be definitely ahead of Arsenal's Vela and possibly also ahead of Blanco in the running to be striker-of-choice for the Mexican national team, even after just four matches.
...he's arguably worth qualifying on that alone. However, Mexico have a busy schedule coming up, and are due to play seven internatonal friendlies before the World Cup and three games at the World Cup, If he plays in most of those games, I can't see the work permit application failing. I'd see it as harsh to say "but that's not 75% of the past two years!" when he was 19 at the time those two years began, especially if he manages to continue his current form (and obviously I'm praying he does!).
I dare say being a highly rated player for the Mexican team (17th in world by FIFA) is probably a bit better than being a highly rated player for the Angolan(86th)/Chinese (84th) team, who couldn't even manage top 70 and therefore wouldn't make any of the requirements at all.