Do I have a case for age and/or medical discrimination?

Hello, I was recently terminated from a salaried position in Tennessee. This came shortly after the hiring of a new General Manager, he started January 2018. Until the new GM started I had never had any problems/issues with the company or the former GM. As a matter of fact I had been given two very substantial salary increases within the last eight months. The reason given for termination was poor performance and failure to meet expectations. I was terminated by the GM with the Shop Manager present, afterward, the Shop Manager walked me out. When we were outside, the Shop Manager said "we both know that was BS, if you ever need anything just let me know and if you want me to I will write you a letter of reference", he is writing one this week. Also, this termination happened on Friday before I was going in for scheduled spinal surgery on Monday whereby I expected to miss the next four weeks of work. I'm 56 years old and the GM is approximately mid thirties.