Your priority date must be current when your I-485 is filed.
If the priority date becomes current while the I-140 is still pending, the I-485 may be filed without waiting for I-140 approval.
Dependent children must be younger than 21 to be eligible for a derivative green card. However, the CSPA has a provision that allows some over-21 children to qualify if they were under 21 when the I-140 was filed.
PD: Jan 2003 (EB3 rest of world)
I-485 Approved: July 2007
I am a layman, not a lawyer. What I write here is not official or professional legal advice. In addition, my answers on this forum are specific to the scenarios discussed in each thread and should not be generalized to other situations.