I was 5 or 6. "Star Trek" was in syndication in the 70's and my brother, John, and I used to fight over what we'd watch at 6pm. He was fourteen years older than me. He wanted to watch "Star Trek" and I wanted to watch "The Six Million Dollar Man."
John always won.
Needless to say, he turned me into a Trekkie and I never looked back. When TMP premiered in '79 I was ten years old and he took me to a matinee. We both had a great nap during the film.