Late 70s TOS syndication, I'm guessing 1977 or so. We didn't have cable but my dad could squeeze a dozen extra channels, sometimes with poor reception with his technical skills. I wasn't a "Trekkie" yet, but I do recall not having control of the TV at that age (being the youngest) and so I would get "voted" down when I wanted to watch it.
Later on I found my oldest sister watching TOS at midnight showings after she came home from work. I started to do the same when I got my first 13" TV in my room. It was actually during Saturday, late afternoon double rerun showings that I remember having a "revelation" about how good the show was, and I became obsessed. Soon after I saw my first ST movie in the theater, Star Trek III. I started buying memorabilia. The rest is history.