Where is the actual source for that claim?
That site links to https://www.fda.gov/vaccines-blood-biologics/coronavirus-covid-19-cber-regulated-biologics/pfizer-biontech-covid-19-vaccine
but that site says:
Pfizer-BioNTech COVID-19 Vaccine (2024-2025 Formula)is authorized for use as follows:
Individuals 6 months through 4 years of age:
Unvaccinated individuals: Three doses of Pfizer-BioNTech COVID-19 Vaccine (2024-2025 Formula) are administered. The first two doses are administered three weeks apart. The third dose is administered at least 8 weeks after the second dose.
It also says 6 months old, not 9 months old.