A "Performance Improvement Plan" (PIP) is a written set of requirements that must be accomplished in order to avoid termination of employment. I don't see anything in your question that suggests a PIP.
Concerning a remedy for a supervisor's apparent duplicity, there is none. The remedy is for employment discrimination (race, color, nationality, religion, sex, age or disability). Your age, without more does not amount to unlawful discrimination. The typical age discrimination action is proved where an employee over age 40 is terminated, and replaced within 90 days by a significantly younger employee. This can be amplified in business organizations where the workforce is generally younger, or there is some emphasis on physical appearance).
If you can think of something that you believe may relate to unlawful discrimination, I'll be happy to provide further commentary. Otherwise, it may be time to "dust off your resume" and start looking for other employment.
I realize that my answer may not be exactly what you were hoping to read. However, under the circumstances, the best that I can do is to explain what the law is and is not, so that you can avoid expending valuable resources looking for answers that do not exist, and concentrate on the options that are actually available.
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