Hmmm...
Lao Fu Zi,
Gigantor, and
Doraemon are the earliest I can think of. This is back when I was five, so obviously I didn't buy the anime personally, however we did own the anime.
The first actual purchase of an anime would have to be the first generation of
Dragonball Z movies, the first probably Ora no Gohan o Kaese!! (now known as Dead Zone) bought on a Laser Disc.
Mmm Laser Discs, now those were the good old days.