Gmail since 2002 or something. Steam account if emails don't count.
Edit: Wow account could be older than steam account. I honestly can't remember.
Edit2: Yep, wow account is a 4 years older than my steam. Turns out I lost my first steam account that did not really have any games on it and instead of recovering it I just registered a new one. Doing this research of my own history was a questionable use of my evening but apparently necessary to get it out of my head.