its literal translation is carriage. Term used in the 70s and 80s in Spain appearing in several dictionaries of slang of the time. Into one appears as just homosexual man, in another as old homosexual man, but in others, as in Cela or Cardin dictionaries, it appears as a middle-aged gay man with money. It seems the term is associated with another gay slang term, well known, which is Chapero, derived from Chapista, with slang meaning of hustler, and with the literally meaning of person who works with metal sheets, a panel beater.
According to the DRAE, Carroza, in addition to the vehicle, means iron frame, and it is with this sense where the Chapero comes into play since he is working with the metal sheet of the iron frame. The Chapero works with the Carroza, or said of another way, the Chapero is making sex for money.
The term carroza is also used to refer to a old or outdated person without having any sexual connotation, but we do not know which of two slang was the first and the origin.
Related Portaviones (aircraft carrier, bigger than carriage, a superlative for Carroza), Chapero (huster).