I have the feeling that it is fairly recent. When I was a kid, I think that nobody used it regularly, then it started to be used on the radio and TV, and then, when I came back home after having spent 8 years abroad, I was surprised to hear it used by the average citizen.

I am not fond of it. It is heavy and in most use cases, doesn't bring more information than 1-12, because the context makes generally obvious to know if we're talking about AM or PM.