ADEA Protections

I see the ADEA and Older Worker extensions protect those who are 40 years and older. Our company is going through a RIF process and I have clear documentation explicitly targeting older workers (as I am both part of administering the process as well as a potential target).

My question: 40 years old at what point? I will be 40 prior to any final separation date, but likely would be notified prior to turning 40. Certainly the overall RIF targeting process takes months and would have occurred prior to my turning 40.

I have no evidence, but would not be surprised to find people are targeted at 39 explicitly to avoid ADEA.

I have searched to find any law, expert, etc. that has an idea as to when one would have to be 40 by in order to be covered by ADEA.

Does anyone have any idea if the specifics of what one would have to be 40 have been tested? Any guidance?