Current PRs and when they were set:
Mile: 5:12 set in high school on a lot of soccer and not much straight running. I probably weighed 155 or so
5k: 20:06 Set two years ago on probably 25 mpw and a fair amount of cycling. I probably weighed 185
10k: I've never really run a hard 10k somehow. Go figure.
Half marathon: 1:35:47 set last year following the Higdon advanced half marathon plan. Catch was that I was a fatass at 190 lb.
Marathon: 5+ hours. Forget this. I botched an Ironman really badly and waddled for 26 miles. Doesn't count.
Current situation: 29 years old. Almost no running in 2014. Was very focused on mountain biking. Weigh 175, and currently dropping weight. My general plan was to just build miles through the fall to 40 mpw, decide on a training plan in January or so, and do a spring marathon, aiming for 3:30 or so (that goal can be modified a lot depending on what training tells me).
Basic question is, though, is running in the 3:00 range reasonable within the next two years for someone with my background assuming consistent focus on running and not too much bad luck?