just apply don’t think too much if his case is approved from uscis the chances of getting an answer before he turns 21 is very high

no one can tell how much time uscis can take to approve the case it varies and depends on circumstances sometimes they approve very quick somtimes not but if he passes the uscis the nvc will fore sure contact him very quick because they are giving 75% of chances to the f2a category each year and 25% for f2b

@Mariam Nassef Here's some info! Hope this helps.. The Child Status Protection Act (CSPA) of 2002 helps certain immigrant children maintain eligibility for US immigration benefits if they turn 21 during the application process. It was enacted to prevent children from "aging out" due to visa processing delays. They will freeze his age . Even if he's 21 he will still be considered minor. All the best