回复：Help -- Immigration for sister and her son

I am planning to file I -130 for my sister's family. Her son is 15 years old.

By the time they get approved, her son will be 25 years old. Can her son still get to join if not married at that time?
-Depends on how long your I-130 will be approved. Based on the "Child Status Protection Act" (CSPA), CSPA age = the child age at the time of the Priority Date is current - the pending time of I-130. If CSPA is less than 21, the kid can join her mother's GC application even if his age is > 21.

See a relevant artilce: http://www.hooyou.com/ageout/index.html

Will filing I-130 affect her son to get F-1 visa if her son want to apply schools in US in 3 years?
-No.