Things like that is just what makes the immigration system so corrupt. I mean what's the difference between if you came at 15 or 18. Who's to say that you enter the the United States at 18. What is the difference between that and entering at 15. I mean who wants to leave the family and not enter the United States. I mean what do you tell your parents, that I will become illegal if I overstay the visa. Would you defy your family knowingly that you will be undocumented within time. That's the parents fault and not the child's, just like a 15 year old would not even ask to stay back because he doesn't have the knowledge about overstaying in the United States would become undocumented within time. Where as 100% of the time an 18 year old would have some proper knowledge about how the system works in the states.
I believe they need to have exceptions for people who can prove they meet all of the requirements except for the age limit. If they can prove they are of good standing they will be eligible to apply. These terms of being able to prove your in good standing should be determined by a group of people if this were to go into effect.