I can't remember NOT growing up with anime. Whenever my sister was babysitting me she would watch anime, though I vaguely remember Toonami and watching Dragonball Z. I think I was six or seven maybe? Also ended up watching Outlaw Star followed by Cowboy Bebop =) then after being introduced to Trigun, I have never looked back. Oh yeah, I'm seventeen now.
I started to watch Nauruto when i was about 10, didnt know other animes or what it was in general. But started this year, when i was 14, to really watch Anime.
I've watched anime all my life although I didn't know it was called anime back then. I always called it cartoons -.-
It was when we started having internet connection that I really knew things. So...grade 4, I guess.
Anime was a lot earlier for me, my first was probably Sailor Moon at the age of 10 or so..? Possibly younger, I'm so old that I can't remember that far back anymore
Manga was only recently though, I think the first one I actually started to read, and have kept reading to this day is Loveless, and I only started that one last year