The other answers that you have received are basically the same facts that I would have supplied as related to qualifying for Boston. However, I noticed that nobody mentioned that there are approximately 5 bajillion marathons held over the course of any given year with at least a dozen in Massachusetts. I assume that you ran in the Run to Remember 1/2 Marathon, which was my first race longer than 5 miles when I ran it in 2005, about a year after I started running. It was also the event that let me believe that I could qualify for Boston, with a bit more focused training. I trained independently, without coaching or peer support, instead relying upon advice and training plans from websites and magazines. And though I did not succeed in attaining my qualifying time (3:10) in my first attempt...not be a long shot...at the 2005 Hartford Marathon, I did learn from my mistakes in training and racing strategy and execution.

My qualifying time did come for me, at my 4th marathon, and I was able to officially participate as an unaffiliated runner in the 2007 Boston Marathon. It is a special event made all the more so by being the local hometown race. I can attest to the validity of the offered advice of targetting 2-3 years out from present for your Boston Marathon attempt.

But if you just want to run a marathon, I would recommend picking a flatter, more entertaining, "destination race" such as the many held in Florida during January or February or one of the produced events for that first experience. A fun and successful first experience will help keep you motivated to stick with running and come back to try again.