Prove it. I’m retired and never heard such a thing. Also, if you recall, Scoyus rejected the stolen valor laws. People can dress as they wish.
No they can't. Retirees are subject to the UCMJ and must respect the articles governing proper wear of the uniform.
http://www.ucmj.us/sub-chapter-1-general-provisions/802-article-2-persons-subject-to-this-chapter
Article 2 of the UCMJ:
(1) Members of a regular component of the armed forces, including those awaiting discharge after expiration of their terms of enlistment; volunteers from the time of their muster or acceptance into the armed forces; inductees from the time of their actual induction into the armed forces; and other persons lawfully called or ordered into, or to duty in or for training in the armed forces, from the dates when they are required by the terms of the call or order to obey it.
(2) Cadets, aviation cadets, and midshipman.
(3) Members of a reserve component while on inactive-duty training, but in the case of members of the Army National Guard of the United States or the Air National Guard of the United States only when in Federal Service.
(4) Retired members of a regular component of the armed forces who are entitled to pay.
I'm a retiree too.