You are eligible for NEET 2022 as you are completing 17 years in January 2022, and the requirement states you to compelete 17 years by December 31st of the following year, in which you are appearing for NEET.

Technically on December 31st, 2021 you would not have completed 17 years, or perhaps thats just a difference of a day so you may clarify this from the NTA. So you might be eligible to appear for NEET 2021, subject to clearance from the Exam Committee.

For more information do follow the link below

https://medicine.careers360.com/articles/neet-eligibility-criteria/amp