谢谢8老师的详细解释.但我还有一个问题

My son's 18th birthday is July 20. Our 5 year green card time is July 15 this year. According to 90 day's rule, we can apply now. Obviously he's < 18. But when the officer starts to handle our file, he may be 18 already. My question when do they start to count his age, now or then? I wish the answer is now, so we only need to pay fees for two (me and wife). Is that correct interpretation?

Thanks again teacher8.