I think I've linked Linkin Park the longest. I'm no longer a massive fan but I can still listen to their stuff and rock along. "Numb" was the first piece of music I learnt to play when I got my first keyboard .
Papa Roach were my favourite band for 4 years, however I pretty much stopped listening to them after their album The Connection came out as I didn't like their new style
Not gonna lie, the first artist that I actually liked was Eminem, since Not Afraid, as he was always a fairly angry guy in his raps, so I could really relate to what he says when I'm going through hard times.
It's either David Bowie or Outkast. My dad got me into Bowie when I was about 8 or 9 but I had only heard the singles and wouldn't have said I was a massive fan until I was about 15 and my music taste started to develop a bit more. But he is the only one really I can think of where I liked some of the work at my youngest age and still like now.
I'd say Outkast though as they are an act I was fanatical about first which I still am now.
I like them both for their eclecticism, reinvention and originality. Both of them have incredible discographies and in my opinion something for everybody which is why I think I've never grown out of their music as different styles and records have appealed to me at different ages.