I see this topic brought up quite often. I'm wondering what are the requirements, in terms of push-ups and sit-ups, for entering the program? I know I'm going to sound like an ass but with all things that are required to either get into aviation, OCS, PLC, whatever, push-ups, running, and sit-ups should be covered. It shouldn't even be an issue. IMO, you should be able to bang out the max or close to it without even thinking. It definitley gets harder with age but in the beginning, it shouldn't difficult at all.
However, for some advice so I'm not ripped apart too much, try the pyramid routine. Example, start off with 5 push-ups, 10 sit-ups, 3 pull-ups, 5 dips. Next set, go with 7 push-ups, 15 sit-ups, 5 pull-ups, etc. Continue to your max, then start down and continue where you began. As it becomes easier, either increase the number in each repitition or increase the sets.