Child must be younger than 21 years old. This means 0-20 years.
Child must be unmarried. Being engaged (naamzad) is ok.
If step-child from another husband/wife, then the child must had been under 18 years old at time of marriage in order to qualify for derivative status visa.
If you were under the age of 21 at the time your parent filed Form i-360, your age is frozen as of that date and you will not age out. Meaning that even if you turn 21 years old or older, as long as you remain unmarried, you will be eligible for visa under your parent’s SIV case.
WHAT ABOUT 21 YEARS OR OLDER CHILD?
Children that are 21 years or older are not eligible to be issued SIV visas under the parent’s case. However, there is an exception. If during submitting form i-360, the child was under 21 years old and unmarried then the child is eligible under the Child Status Protection Act (CSPA).
At time of submitting i-360:
Child under 21 years old and unmarried = Eligibile
Child 21 years or older = Not eligible
Child is married = Not eligible, even if under 21 years old.
Child is engaged (naamzad) and under 21 years old = Eligible
The child must remain unmarried before immigrating to USA.