I think @LaffingBear has hit the nail on the head, especially about the issues not being reported at the time they occurred. If you are serious about this, please heed the advice of seeking council.
One question I have is... was there any severance provided? If so, you likely waived any rights to legal action. That said, in the case of age discrimination you have 7 days to revoke a signed severance.
Based on the information provided, the one thing that most strikes me as odd is a performance based termination without any prior discussion. Most companies, especially large ones, will document performance issues in excruciating detail and put an employee on a performance improvement plan prior to termination. It's worth noting that in Nevada you have 60 days from termination to inspect your personnel file. Perhaps that is your first step.