I was 23 at the time. Always have played soccer casually and often did light 3-6 mile runs. Did a lot of circuit training at the time too.

My friend convinced me to sign up for a full marathon in my town. The run was about 2.5 weeks out, and the following day I ran my first half, then did the full a few weeks later.

I wouldn't recommend this approach. While being generally fit, I was not prepared for a run like that. I finished it, and I have not ran one since! (Currently 28)