I applied for my sister and her family for greencards and they were approved after 10 years (I-130). Her only son was 18 when I applied in 2001 and the application was processed approved. It is 10 years later, NVC has send me an AOS and application for both my sister, her husband and her son (who's now 28 years old and unmarried). I paid the fees ($88 and $404) for all three of them but I am uncertain if he can get a visa since he's an "unmarried child over 21" now ?? Should we proceed with his application ? futile or am I misunderstanding the law?
I appreciate your response and time regarding this matter.

