The age factor that you should have used to determine your 2021 RMD comes from the appropriate table in Appendix B of 2020 IRS Pub 590-B. (2021 Pub 590-B has not yet been published but will have identical tables.
If you are instead trying to determine your RMD for 2022, you'll need to use revised tables that so far have only been published in the Federal Register: https://www.govinfo.gov/content/pkg/FR-2020-11-12/pdf/2020-24723.pdf
