Only by going outside the US because once he turns 18, he starts to accrue unlawful presence time and then it is not going to be possible at all to legalize status within the US due to the unlawful entry. But even if he goes outside the US now, the sister's petition will not help him immediately. It will take about 10-12 years. However, if he is outside the US and is eligible for college, he can try to get a student visa to come to the US and attend college.
Answered on Jan 06th, 2012 at 10:30 AM