Hello and welcome to JustAnswer.
I'm sorry to hear about yoru situation and hope I can help.
Unfortunately, as an at-will employee, you can be termianted at any time for any reason with or without any prior ntoice.
This stems from the employment at-will doctrine, which is codified in California Labor Code Section 2922, and states:
"An employment, having no specified term, may be terminated at the will of either party on notice to the other. Employment for a specified term means an employment for a period greater than one month."
However, if you believe that you were discrimianted against on the basis of your age, then you should file a complaint with the Equal Employment Opportunity Commission for discrimination in violation of the Age Discrimination in Employment Act (or "ADEA").
You can file a complaint using the instructions available online here:http://www.eeoc.gov/employees/charge.cfm
The EEOC will investigate the complaint on your behalf and either file suit on your behalf or issue you a right to sue letter so you can
pursue your claim against your employer through a private attorney.