There is no lawsuit. The McDonald Douglas framework or the "but for" framework of a lawsuit will be defeated , in my opinion.
Age is a factor if there is no company wide resource action. "But for" is a factor if there is no company wide employee reduction.
The right to work has about three exceptions and one where the letter you received is "you are permanently" part of the resource reduction will not survive the scrutiny of age discrimination just because you are over 40 when you were told you were "permanenly" selected to not work for IBM anymore.
Anyone thinking they are going to sue, should Google Supreme court decisions and appeals court decisions regarding the McDonnell Douglas framework and the "but for" framework of age discrimination lawsuits and see how you will not survive it with the letter and the information on how the selections were made.
A company can legally law off workers and IBM has shown it will do it across the corporation body
Re-read the resource action notice.
IBM Legal has it covered, in my opinion.
That means not eligible for rehire, permanent means permanent.
It means not eligible for reassignment or to be selected for another position within the company.
Take the money, go back to school, get certified in some skill and apply at another company.
Technology changes and so does many other skilled areas. Learning to communicate in this new environment using proper pronouns and excluding use of certain past beliefs is key and currently being taught to the younger generation who replace older generations.
I am not typing this to anger anyone.
I do suggest anyone thinking of refusing to accept the severance payment consider how they will feel when there is no attorney that will touch suing IBM when the layoffs were company wide, every department, every age, every span of years worked, where a company is not required to keep older workers just because they have a lot of them
I bid you a better future as you start on a journey no one wants to take.