回複：但遞交485時， 他兒子隻有19歲， 因該是合乎要求的。 請指教

You will find the denial reason in the Denial Notice. But as far as I know, for employment based category, the dependent has to get I-485 approved before age 21, not the time to file the I-485. But for family based category sponsored by a U.S. citizen, it is Ok for a dependent to file the I-485 before age 21, not the time for the I-485 approval.