i want to run a marathon, and im 12?

The risk of getting injured while you're still developing far outweighs the reward of completing a marathon. And yes, you'd also be looking at some significant mileage increases to truly prepare -- at least a weekly long run in addition to whatever you're doing now.

It's pretty unlikely you'd be able to safely monitor and alter your diet as you'd need to for marathon training, too. Marathon training can also become time consuming, and at younger ages, your time is usually better spent with school, friends, or other activities while you have the opportunity.

Anyway, there's an age limit in almost all marathons for good reasons. Many half marathons have more lenient limits, however. If you absolutely positively want to train for something, I'd find one of those. Otherwise youth is often viewed as a good time to work on your speed at shorter distances rather than your endurance in longer ones. And if you do get injured training for longer ones, the injury can often become nagging for a lifetime -- it's just not worth it.

What do you do? You wait until you're older, and you find other goals to work on now instead that you won't have the opportunity to pursue when older. There's not really a good reason to "want to" run a marathon when 12 that outweighs all the negative risks.

As others have said a marathon is 26 miles nonstop, you don't have a week to run it. I'm sure you knew that though. Anyhow, most marathons won't let someone who isn't even a teenager yet run in one because it can mess up your growth plates or something. I suggest finding a half marathon. Why? Because they are only 13 miles, you don't have to be 18, and because it's good practice. Maybe when your 17 or maybe even 16 you can find a marathon that will let you run in it with your parents' permission. Good luck!

A marathon is 26 miles AT ONCE. Not a week, you don't have a week, you have to do it in a matter of HOURS.

I'm not saying you can't do it, I'm just saying the amount of running you do per WEEK now is equal to what you have to do in a few HOURS. So you may want to train up a bit more, maybe a half marathon (13.2 miles)?

get some one else 2 run it for u love. Or if that fails run it with an adult they should let u then. Good luck tryin anyway:-)