I thought this might be interesting; to hear everyone's stories of how they began their journeys.
For me it was as a fill-in for a gym requirement. After my sophomore year of high school I left to attend college full-time, and the courses I took at the local university also counted towards my high school diploma. I would actually amass enough credit to graduate from high school after my junior year. However, since I was at college full time and never set foot on the high school campus, I didn't have any gym class. The solution my principle came up with was that I could work at out at the school's gym, have a trainer sign off that I had been there, and that would count as my gym requirement.
My father had worked out for years at this point; he started when he was in his mid teens, at first running/sprinting. When I was young, in the late 80s we were too poor for him to afford a gym membership so he bought a weight set, welded his own squat cage, and even rigged up a cable cross & cable row in our basement by running ropes through small holes he drilled in the basement rafters. Looking back it was fairly genius.
Being a teenager though I was trying to do the 'independent' thing and didn't want to really workout, since that was 'his thing'. As such I had never worked out. My first ever workout was in February 1999, and as soon as I started I was kicking myself for not starting earlier. I loved it. I was also incredibly unbalanced in my approach; hitting my legs every couple of days, and largely ignoring my upper body. I didn't do anything more than a few sets of chest-pressing for the first 2 years I worked out. Incidentally my dad is still my favorite person to talk to about the gym. Even though I've surpassed most of what he did (aside from his ridiculous 250 lbs. cable rows in sets of 10 at a bw of 170) he still has some of the best advice I've heard.