Hello 2-Caps!
I have been searching. The earliest use of the term, found so far, appears to be 1961. Something called Korvette Malls announced that they were creating their own record label
and that they would probably concentrate on concept albums such as singalongs!. It was apparently in Variety. I found it on a discussion page, and you know how reliable those
things are.
I think there may be a difference between an album that is themed and an album that is narrative.