Its interesting I never got into computer hacking until later when I was in college. In high school, I had a neighbor who was really big into phone phreaking. We had hours of fun building black and blue boxes, getting free long distance and calling people in random countries.

Probably the coolest thing was my neighbor somehow managed to get his hands on two master keys for the high school. He had a buddy at a local hardware store duplicate them (highly illegal) and we spent many nights prowling the high school, opening doors nobody could and exploring every inch of that place. Thankfully we never got caught, but I look back fondly at it as the start of my career hacking stuff.