Are you referring to Basic Training/Boot Camp? Or afterward?

I was refering to Basic/Boot camp.

If you can't make the grade after a certain amount of time, they'll send you to fat camp (they call it the "Warrior Spirit Company" at Ft Knox) where you will do PT all the time until you CAN pass the APFT. And you will not leave Basic until you can do so.

i heard they had an advanced S/S.

The Army also has SOTIC (Special Operations Target Interdictions Course), but you have to be within a Special Operations unit, ie 75th Ranger Regiment, Special Forces, to attend. Other services send their guys as well. It's longer and more involved than the school at Benning. So if you're thinking of enlisting under and Option 40 contract (Army) and manage to make it through RIP, that is an opportunity that can present itself as well as the other schools (Marine S/S, RM, etc). But like I said, for now, focus on your 25 metre target, and that's enlisting, getting through BCT/boot and becoming the best soldier/Marine you can be ... and worry about the rest later .. you'll have plenty of time once you get in .. and if for some reason you don't like it, or can't get to where you want to be .. it's only four years.

Not that it's much of a concern, but what if you simply cannot do the given ammout of pushups or situps?

Now, right here you've gone and gotten your mind twisted up and confused. If you wonder about things like that, it's going to take away from your drive. You don't want to be a "no go" on anything .. so while you have the time, hit the gym, eat healthy .. run, run, and run some more. Don't stop at 3 miles, make it to 5 .. then 10. Ruck as well, get a pack, start at 10lbs.. increase the weight and distance you ruck. Don't stop at 50 push-ups, get to 100 .. don't stop at 10 pull-ups .. make it to 50. Push yourself, train yourself .. and if you're in great shape, the physical aspects of basic/boot will be a breeze for you and will help in taking some of the stress away. The Navy EOD warning order is one of the best programs to use, it's a good tool to help you progress. Here's the link:
http://explamphibian.home.mindspring.com/eod/eodwo.html

However, be prepared to be punched in the face, choked, etc. I know 2 guys who just got back from Parris Island a couple weeks ago and they said it happened all the time. Plus the fear thing. It lasts, believe me it lasts! But you can make it through! That's the biggest thing. These guys said they saw people wetting their pants in front of the DIs almost every day, literally.

Sounds like an episode of Scare Tactics to me

Sounds like fun... very rarely to i have to time to toughen up. But when i do, i go all out. Although i don't like this bit about little girls peein' in their pants... i didn't realize such young'ns were aloud in the military.
'Course... i should probably shush up until i see how hard it is eh?

Yeah I really don't know about that. the only time I've heard first hand of anyone pissing themselves in training was from my friend who just went to CDQC (Combat Dive Qualification Course), and there you're in the water all the time, so it's kind of expected you'll use it as a latrine.

Im 14 and i wanna be in the Marines, actually, i WILL be in the Marines. I think that if you REALLY wanna be a sniper. then i suggest you go into the Army. Unless, you want to be a Marine more than a sniper. Because the Marines dont revolve around MOS's. they revovle around you wanting to be a Marine. they will make you one. You have to be ready to be in the Marines, you have to WANT it. Its not like the Army, you dont just say, i wanna go in the Marines, out of nowhere. Its a serious decision. If you wanna be in the Marine Corps for the sniper program, dont get me wrong they have an EXCELLENT program. But i think that if thats all you want, that you should consider the Army.

Hey SemperFi - You say you're 14? What in all of your 14 years of life exactly qualifies you to even begin to compare the USMC with my Army? I have known many Marines, in fact my son is a Marine and I spent 22 years in my Army. I respect most Marines because of the way they carry themselves. Real Soldiers and Marines don't go around trashing other services, they don't try to prove themselves with words. They prove themselves through their actions. If you actually do expect to try to become a Marine I suggest you concentrate on doing just that.
I have seen both Marine Corps and Army training up close and personal and I can tell you that neither one is a walk in the park. They are not meant to be easy. They are meant to produce the finest, best trained, and best equipped fighting men and women in the world - bar none. Whether you wish to become a soldier, a marine, a sailor, an airman, or a coast guardsman, I think you'd better have a bit of respect for those that have gone before you and have already proven themselves though their actions. If you have a preference for the Marine Corps, that's all well and good but, one word of advice - drop the disrespect, there's no place for it.
Maybe you've heard service people calling each other dogface or jar head or the like. You should keep in mind that these people have earned the right to joke around with each other. Unless you've been there and done that, just listen to them. I know you're just 14 and I hope you take what I said in stride and as words of advice.

Sigh. My nephew went to the fat farm. I offered to work out with him before he shipped, but he would never show. And he FAILED. This fatbody got rejected from the fat farm, in the Navy.
Well, luckily he can flip a mean burger.