You are eligible to make HSA contributions for any month that Medicare is not active. Part A Medicare starts the month you turn 65 (or, if you turn 65 on the first day of the month, Medicare starts the first day of the previous month). If you enroll for part A late, it is retroactive 6 months from enrollment date. That means if you turn 65 in February 2022 and enroll in Medicare in July, 2022, your Medicare will be active as of February 1, 2022.
That means you are HSA eligible for only 1 month of 2022, and your contribution maximum will be $387 (if covered by a single HDHP) or $691 (if covered by a family HDHP).
You can contribute this money at any time in 2022 that is convenient. You may even contribute after you turn 65 and after you have Medicare. What counts is the amount you can contribute, it doesn't matter on what date you actually make the contribution.
