It was the early part of 1998, because it was toward the end of 6th grade. So I would have been 12.
I've been around computers since I was 7, though. My mom had a DOS machine she'd gotten through a correspondence course, my elementary school had a handful of Apple II's and Macintoshes, and my grandfather had a Packard Bell that ran Windows 3.11 for a few years. We got a Win95 setup in 1995* - that computer is still functional, nearly 16 years later (although rarely used). Most of the Windows-based computers we used at school also ran 3.11 until I got to high school, although there were three or four Win98 machines in my 7th grade comp class.
*IIRC, it cost somewhere around $3-4K...Pentium (not sure which one, could have been the P54CS or P55C - either a Pentium-133 or Pentium-166), 16MB RAM, 4GB hard drive. It was this computer that I first used the Internet on, via AOL.