I agree, it is likely because of aging out. The CSPA age protection cannot be calculated exactly, since the Priority Date is not yet current, assuming you are from the Philippines. The current PD is 02/01/2004 — 10 months before your PD.
it is clear, however, that the older “child” has aged out from CSPA protection even if the PD was current as of this month. The petition was pending approval for 4 years, 5 months, and 29 days. So, as long as a visa number is available (I.e., the PD is current) before they turn 25 years, 5 months, and 29 days old, they would qualify for the visa. As of October 1, 2024 (this month), the older child was 25 years, 7 months, 10 days old and has aged out.
There is still a possibility that the younger one will qualify, although it will likely be close. He/she is currently (as of Oct 1), 21 years, 9 months, and 20 days old (although you said 22 years old). If a visa number is available in the next +/-3 years 8 months or so, the younger will not age out.
The PD has to advance more than 10 months before their PD will be current. Historically, the F-4 PD moves very slowly, if at all, during a Fiscal Year. For example, looking at the F-4 PD for Phillipines on October 1 of the last five years, it was:
Oct 2024 2/1/2004
Oct 2023 8/22/2002
Oct 2022 8/22/2002
Oct 2021 8/22/2002
Oct 2020 1/1 2002
So, for 3 years prior to this year, the PD did not move at all. It made a large jump this year, but it is unlikely to do so again.
I would likely send an e-mail to NVC, asking about this, especially highlighting that the younger “child” has not yet definitely aged out of CSPA protection.