My first 12 or so years are basically the same as most other people. Listened to whatever was popular in the late 90's and early 2000's in the UK. Moving onto Hip Hop as Eminem became a huge star. I think the first music I started listening to which wasn't the same as everyone would be The Stone Roses. This led me to other British rock bands like Oasis, Suede, Smiths etc. when I was about 14.
At around 16 I moved onto listening to popular 'indie' bands like Kings of Leon, Cage the Elephant and The View through XFM, a radio station based in Manchester which was a favourite of my Mums. Looking back I was into this stuff for far too long, and I'm disappointed at how long it took for me to bother looking for other music that wasn't presented to me. Probably because I liked most of it (and still do). Though I did pick up a few greats like Doors, Stooges and others in the process.
So I think it wasn't until I was 19 that I looked for a site that would record my listening history. Of course that led me to last.fm.
The state of this:
TomClancy11
Around 2010 I discovered theneedledrop who, to this day, is by far the biggest influence on my tastes purely by bringing attention to the world outside of popular music.
Gets Spotify, signs up to musicbanter. Rest is history.