I saw my first episode—The Cloud Minders
—when I was 4 or 5, one Saturday afternoon. Started watching more live action Trek, which was irregularly scheduled, and then totally trekked out on the animated series when it debuted. Live action Trek was often hard to come by in the seventies, often late at night on the weekend, but sometimes during the day, and occasionally in the afternoon throughout the week. When it was on late at night, my parents would wake me up to watch it.
The Squire of Gothos
was the last live action episode for me to see for the first time, and I was a teenager by the time that came around. But by then I'd seen other episodes multiple times. Eventually, VCR came around.