Assuming he had no contract he was an at-will employee and could be fired for no reason or any reason except for an illegal reason such as race, relgion, age, etc. Given the facts you mentioned he should speak with an employment lawyer.
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If, in fact, it can be shown that your father was terminated so his duties could be taken over by a younger worker and age was the reason for his termination, your father may have an age discrimination case. I generally advise in these circumstances that the employee file for unemployment benefits before taking any action against the employer so that the employer documents to the Unemployment Board that the termination was for lack of work, thereby foreclosing the employer later claiming the discharge was for misconduct, which would be a defense in an age discrimination case. Your father should speak to an employment lawyer asap.
Your father could have an age discrimination claim, I suggest speaking to an employment attorney in your area.
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