The worst part is that studies show men in their 50s who lose their jobs have only one in three chances of finding a similar one at the same income. But you're also right to know I'll be urging you to look for the opportunity in this problem. First off, let's consider the lawsuit. The chances of winning are slight, and to fight this one would very likely require you to stay mired in your anger and sadness for years. You'd be spending precious time looking backward rather than forward.
Some people seem wired to dwell on injustice and old hurts and tell the sad stories over and over.
You don't strike me as that kind of person, and I wouldn't recommend letting this experience turn you into one. It would be far better to end on a positive but tough negotiating note with the company, by squeezing out the best separation package and benefits you can, and then get on with doing what you really want to do. I'm struck by your comment about retiring early to do mechanical work. You wouldn't get rich overnight, but if you played your cards right and combined a decent package with some underwriting projects plus several days a week of mechanical work, it would be a fine start. And it would be so much better for you than trying to fight the downsizing or even staying on if they offered you the chance.