Full Marathon

It can be done in a year. You might have a more pleasant experience if you wait even longer, more like building up slowly over 2 years though. But it can certainly be done.

Instead of trying to run as long as you can, you might have good luck with a walk/run program as you build up your mileage. Jeff Galloway has a lot of good walk/run programs for free on his website. You can add on mileage more easily that way, and then the speed with naturally follow as your endurance improves.

The first time I registered for the NYC Marathon, I could not even run for a mile. I was also registered for the Chicago Marathon. Joined a local running club and did a 10k training plan and after I was able to easily run 6 miles, joined the running club's Marathon 18 week training program. The plan that the running club use for beginners is Hal Higdon's first time Marathon training plan. Total training time from the 10k train through the Marathon was about 28 weeks.

More details can be found at http://www.halhigdon.com. The program got me through both Marathons and I had a blast. Since then I have run 8 marathons and one ultra. Two more ultras and a trail marathon still on the schedule for the remainder of the year.

I'm about half way to a marathon myself - I've trained for them before but never made it to the starting line due to a series of unfortunate events This time I started with C25k, then did a bunch of 5ks and a half marathon race. Between the half and the start of training for the full (I'm doing Hal Higdon's intermediate), I've got some 5 mile races, 5ks, and a 25k. During the marathon training I've got a bunch of 5ks, 10ks, and a half, too.

You can totally do it, just keep realistic expectations, stay focused, and slowly build your miles. Find and follow a training plan (I made a spreadsheet, I've got every run planned out for about a year [tri a few months after the marathon then another half brings me to next October]) so when you're feeling down or not in the mood for a run you don't talk yourself out of some miles you need, or find yourself wondering what on earth you should do on a given day... It's all laid out. There's something super confidence building seeing the runs climb slowly, knowing you feel good this week, and can totally handle the plan.

I saw a plan on logyourrun.com that was 40 weeks, and it took sedentary people basically from the couch to a full marathon.

I trained for my half marathon for 10 weeks-yes you can do it-but I would work on your speed if I were you (intervals will help) 4.0 mph is typically a brisk walk for most.

and I would not start with a full marathon if you haven't raced in shorter distance races yet.
You should be able to run a full 30 minutes before even considering a half or full marathon.

work your way up-you will get there

good luck

I did my first 10k on July 3rd this year, I made the leap to a half marathon, which I completed this past Sunday. I didn't really train for it, I did a couple long runs a week or two before the half. I was able to complete the whole thing without walking in just over 2 hours. You should be able to do it with a year of training no problem. Just keep in mind to pace yourself at something comfortable. It's not how fast you finish just that you finish.