Assuming a reasonable amount of ability, and you clearly have that, usually a marathon is as hard or as easy as you want to make it. But they are nothing to fool around with. Back in the stone age when I was in high school in Illinois my cross country team typically ran a marathon (Paavo Nurmi in northern Wisconsin) late in August. It was at the end of a full summer where we had 18-20 guys all averaging a minimum of 10-12 miles a day with quite a few 100 mile weeks, or more, thrown in. We also had a good number of distances races over the summer. Summer before my senior year I remember we did at least a five mile race( at Glen Ellyn), a 15 K race (Woodstock to Crystal Lake), a 20 K (Panther Pant in Charleston) and 100 Mile Relay (10 men each doing two 5 mile legs, again in Glen Ellyn). Plus a bunch of 3 mile summer cross country races. Point being that by the time we got to Paavo in August we were pretty well prepared and the race was tiring but not a killer. A couple of our guys, the real distance animals, pushed it a bit hard but for the most part we ran together in a group, kept it cool at 6:50-7:00 minute pace, talked the whole way together and had a great experience. We had 8 guys run between 2:48 and 3:00 in what was essentially a training run. But we all came away loving the marathon and feeling we could do much better next time. And most of us did.
I have also run them when I wasn't very well prepared and they absolutely sucked.
I'm not suggesting that you follow the training I did when i was 16, we were a bit nuts back then, but make certain you have a great first experience. Train really sensibly with the marathon in mind. Make the race as easy as possible by preparing really well. Pick a race where the conditions (course, temp, humidity, etc.) give you the best chance for a supportive run. Pick one where you can tuck in with a sensible pace group and cruise through it at something a bit slower than your training would lead you to expect. Make the first one reasonably comfortable so you want to run more and push your limits next time. And the time after that. First marathons should not be raced when you are in your teens.
One final point, people recover differently from marathons. No matter how much effort they put into them. If you have a track season coming up then stay away from the marathon until you have plenty of time to recover. Don't endanger an important racing season (track or CC) just to scratch the marathon itch. Plenty of time to run plenty of marathons in the future. They aren't going anywhere but we only get a few chances to run in school.
Hope this helps a bit.