I'm very confuse. If say my sister applied for me and my mom for the green card and I'm OVER 21 years old then when my mom becomes resident or (even better) citizen and apply for me as child over 21 years old can the priority date from sister's petition be applied to the new petition from my mom? I know it's possible under CSPA, but CSPA is valid if you were UNDER 21 years old on time of the 1st petition from sister. What about if you are OVER 21 yo. Any reference?