Was instituted yes. By congress who didn’t institute the same for themselves. To say it can’t be done it would be unconstitutional them is correct
But it could be re examined along with congress facing the same limits. Stinks of abuse.
Term limits on Congress were attempted by some States for their own representatives. But they were shot down by the Supreme Court in the Thornton Decision (1995). A constitutional amendment (tough to achieve, and for good reason) would be required.