I am considering an Discrimination lawsuit against my former employer (age/other)

I was brought in 5 months ago to replace someone who was not getting the job done in the role. This person was moved to another role in the company. I was terminated 2 weeks ago with no explanation and only a vague e-mail previously about deferring to others 30 days prior. My boss is not co-located in Texas and as a result I emailed him with my views and the request to discuss the situation, which was never answered. I believe I was treated differntly for some reason, possibly my age. Do I have to bring this action in Texas where I worked or in California where the company is based?? Thoughts??