Under the Child Status Protection Act (CSPA), the child's age is essentially frozen once the I-526 is filed. Once the petition is approved your child's age will unfreeze and the clock on his age will begin to run again. The child is required to seek an appropriate visa within one year after the approval of the I-526. Please consult an experience EB-5 attorney to avoid any potential problems.
The I-526 petition must be filed before your son turns 21 years old in order for him to be included in your petition. Once USCIS receives your I-526 petition, you son's age will "freeze" therefore your son should receive immigration benefits under your petition regardless when the petition is approved. Please consult an experienced EB-5 to fully discuss your case and avoid complications.