It depends...on YOU.  That is, I think it depends on what kind of shape you are in when you start, how your body deals with training stresses, what kind of time and energy you can devote to training, and importantly, what kind of race you want to run. 

How do you feel when you're running?  If you already have days when you feel like you could run forever, then maybe you're good.  If it's a real challenge right now and if you're a person who is inclined to despair or lose motivation due to failure and injuries/setbacks, maybe set a shorter goal. 

If there's not a particular hurry, you can always set your sights on running your half-marathon in a year and 7 months, and then feel really well trained, finish strong and feel great.  It's good to have short and long term goals.  I currently have a goal set to try to acheive 4 years from now, but lots of interim goals along the way.

Just keep running!

"Do you think that 7 months from couch to half marathon is reasonable, or am I being a fool? "

It could be either.  It depends greatly on your training and your goals for the race.  It can be reasonable if you train carefully and progressively, and your primary goal is finishing the race.  You have about 16 weeks (depending on the exact date of the race).  Train to avoid injury.  Work on distance, forget about speed for now.  Listen to your body at all times!

Just for curiosity's sake: what race?

Len

In my opinion you're not a fool at all.  I started running on 2/14/11 and I just completed my first 1/2 marathon this past Sunday.  I did the c25K program, then the bridge to 10k and then the Hal Hidgon's Novice 1/2 training.  I made sure to follow the program closely so as not to over train, and I listened to my body as I went.  I didn't find that the training was inadequate at all.  I was able to run the whole 13.1 (didn't even need to walk for water stops - I had a hydration belt so I was able to keep running).  I made sure that I kept my pace easy the whole time (in the 11mm zone) and afterward I stretched A LOT and rehydrated.  Just three days later I feel fine and I did my first post-race run today (just an easy 2 miles to see how my body felt). Like you, I need goals and I like to challenge myself.  I think if you're smart about it and you don't set the bar too high you'll be fine.  For the record, there were plenty of people completing the 1/2 using the Galloway (walk/run) method.  I know there are people who feel that unless you're running the whole thing it somehow doesn't "count" but I'm a big believer that as long as you're true to your own goals and you're being safe about your training you should be free to enjoy your accomplishments without judgement.  That said, it's possible that I'm one of those over-zealous newbies, so take what I say with a grain of salt, but I did it and I'm pretty much dead average in terms of my conditioning and ability level so I'm probably able to speak for the "normal" person.  I say, if you want to do it, do it.  If you have to alter your plans as you go, be willing to do that too.  Best of luck!  

G.,

You might be quite foolish in other respects, but the goal of a 1/2 Marathon in March is quite reasonable.  The challenge will probably be to get your milage in through the dark of a PA winter. Persevere, though, and you'll most likely do just fine.

I defer to those more experienced with their great training advice.  I can only offer my humble opinion and that would be that competing in half marathons is a process that involves a gradual trasition through other distance races.  However, I also hold the old school reference that training at seven miles a day is not enough either.  I never enter any race unless I have completed ( via difficult routes) at at least double the distance of a particular race.  However, I certainly also understand the desire to participate and finish because every runner holds that sense of pride in accomplishing a particular goal. 

To answer your other question -

I was an off-and-on runner for a couple years before I ran my first race (a 10K).  I ran to stay in shape for other sports, usually less than 2 miles 2 or 3 days a week (max 3 miles but that was unusual).  And I didn't run through the winter.  After the 10K in November I trained more consistently, ran a couple shorter races in the Spring and a half in September.

Len

I have never seem anyone who believes that you double the distance of your race for your longest run before!