Here are some things to ponder when faced with this question.
1. Why is there an age limit period?? Free country...NO??? Soccer phenom signed at 14. Baseball almost as young.
2. Back when the Vietnam War occurred, kids, and I do mean kids, went off to war, literally killed people, did all kinds of drugs and drank all night because the government provided it and then when they came back to the "world" weren't even allowed to walk into a bar and buy a beer, but they were sent off 10,000 miles from home to kill. Same issue now. Soldiers in the Middle East, killing, taking peoples lives, yet there not allowed to play a game professiionally.
One point can be just let them play, others are going to say no, like myself, because I'm selfish. My favorite sport is college football, and this would dilute the level of play, but not as much as you think, but to a point.
3. They may want to make rules such as allowing only cornerbacks and maybe wide receivers come out early.
Just thoughts...