In the immigration categories where a child can immigrate as a derivative of the petition filed for his/her father or mother, the child must immigrate while under 21 years old. Once the child turns 21, he/she ages out and would need their own immigration petition in order to immigrate.
Because most of the categories under which a child can immigrate as the derivative of the petition filed for his/her parent are backlogged, this creates a problem, as the child must be under 21 years old at the time they actually get the green card.
In an effort to partially address this problem, Congress passed the Child Status Protection Act. This act can freeze the child’s age under 21 years old under some circumstances, allowing the child to immigrate with the parent, even though in reality the child is over 21 years old.
For family and employment based petitions, the calculator below will give you an idea of whether or not the child would qualify to have his/her age frozen under 21 for immigration purposes. For the family based petitions, the petition is the the I-130, and for the employment based petitions, it is either the I-140 or the I-360, depending on which one is applicable to the case. The date the visa became available is the first day of the month for which the priority date report shows the visa priority date is current.
The Ninth Circuit issued an opinion that was highly favorable to CSPA applicants. That opinion has been appealed to the Supreme Court, where it faces less than 50% odds that it will be upheld–The Supreme Court frequently overturns Ninth Circuit decisions, and under Supreme Court precedent known as Chevron Deference, courts must defer to agency interpretations of statutes that are ambiguous.
Please note that the final determination is that made by USCIS and/or the Department of State.