Though probably unfair as I was born and raised in Japan, but I guess my first real addiction to anime as an otaku base would be watching Neon Genesis Evangelion on air.
Apart from that, I don't think watching Anpanman, Sazae-san, Doraemon, or other Fujiko Fujio anime like Kiteretsu Daihyakka or 21emon would count persay. Nor would watching things like Arare-chan, Hokuto no Ken, Kinnikuman, CITY HUNTER or Dragon Ball would count either. Studio Ghibli works? Meeeh, not quite there yet either. All of these were more like "everybody boy (maybe some girls too) in my age group watched that as they grew from toddler to elementary school."
OTOH, I did get somewhat a small taste of otakudom as a young child when I wandered near my aunt's place in Harumi where Comiket was back then. As a child all I knew were "creepy looking geeks lusting after Lum-chan drawings made by amateurs." Couldn't quite get that as a 10 year old boy.
Little did I know I'd be one of them when I started lusting after Ayanami Rei doujinshis a few years later.
