Unfortunately, as an at-will employee you can be terminated at any time for any reason (even a bad or false one) with or without any prior notice.
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."
Also, unfortunately, as an at-will employer, your employer is not under any obligation to give you an opportunity to defend yourself, even if the allegations against you are baseless, or there is an explanation (that you didn't have the cash to give for one).
Even if your manager personally disliked you and 'had it in' for you, as long as he didn't do so due to a protected characteristic, you wouldn't have a cause of action for wrongful termination.
However, if you have any reason to suspect that your age was the actual reason for your termination, then I highly suggest that you file a complaint against your employer with the Equal Employment Opportunity Commission for discrimination and wrongful termination in violation of the Age Discrimination in Employment Act ("ADEA").
You can file a charge with the EEOC using the information available online here:
The EEOC will investigate your complaint on your behalf or issue you a right to sue letter so you can pursue your claim against your employer through a private attorney.
I sincerely XXXXX XXXXX had better news to give you, but I hope you appreciate a direct and honest answer to your question.
Please let me know if you have any feedback questions.
If not, please remember to positively rate my answer so I get credit for my work.
Please also rate me highly when you receive your customer satisfaction survey. High ratings ensure that I will continue to be able to answer other customers legal questions on JustAnswer.
Thanks and best of luck!