1963 - prewar interest since I was around 13 - 14, started to subscribe to Hemmings Motor News at 14 after seeing an issue at a friends house whose dad was a collector. I have always preferred prewar cars and euro sports cars to muscle stuff that seems to be most popular with my age group.
FWIW I am less convinced "no" younger people are interested in these cars as my experience recently seems to show otherwise.
Cars in general were a mainstream interest when I was a teen; much less so nowadays but certainly not unheard of.