Probably in seventh grade, when I was twelve. I had an English teacher, Miss Lee, who taught a vocabulary word every day. The word on the first day of class was accessible. I was hooked immediately. Facetious was one of our words, and she must have told us that it had the vowels in alphabetical order. My fascination with words started then, but I didn't focus on panvocalics as such until many years later.
Containing each of the six vowels once (adj.); a word that contains each of the six vowels once (noun).
"Euryvocalic" is coined here to refer to these words; "eury-" meaning "broad", referring to the broad range of vowels. Euryvocalics are a subset of panvocalics (which can have repeated vowels) and of euvocalics (which need not have a "y").