If i do 100 Crunches a day?!

100 crunches is simply too much of one exercise. You should be doing a circuit for you ab routine. An example would be:
Plank-90 seconds
Side plank-45 seconds each side
Reverse crunches-20 reps
Obliques-20 reps each side
Medicine Ball Passovers-30 reps
Bicycle-30 seconds
Ballet Kicks-60 seconds
You would do this routine for 3 sets. However you can't simply jump into a workout and expect results. You should be doing a varied cardio routine with this as well. Such as:
Monday-Treadmill
Tuesday-Bike
Wednesday-Treadmill
Thursday-Elliptical
Friday-Treadmill
Saturday-Stepper
Sunday-Rest
The treadmill is inserted into the routine more heavily because it burns more stomach fat than the other types of cardio machines.

http://exercise.about.com/od/abs/ss/abexercises.htm
Years of personal fitness and nutrition

That's really skinny. Before changing anything, you should go to the doctor and have them check your body fat (BIA). The healthy range is somewhere from 21% - 25% body fat. But exercise never hurts. Building more muscle will help bump you into the healthy weight range and harden and tone your body. With a hundred crunches a day, I would say you might see results in a month or two, but protein plays a large part in building muscle. But be careful, too much protein means some of it won't be used to build muscle and build up in your body as fat.

Figure out how many calories you consume/burn a day (even through sleep) and plan your workouts accordingly. If you want a six pack you need to gradually increase the ferocity/number of repetitions you are doing. You don't want to plateau (you won't get any results after that), so gradually work up to increasing the number of reps you do and mix up your work outs! Don't forget your lower abs and obliques too! They are essential in helping you gain the body results you want (crunches alone won't work out your entire abdominal region).

Worked at a gym, avid fitness buff

When I get pudgy and I need to lose weight I start lifting weights. Even doing that for 3-4 days a week it would take me about 3 months to actually see results and see my body get more lean and tone.

I don't know for sure, but I don't think doing 100 crunches a day would do anything. You need to do other exercises besides crunches.

It took me about 6 months to figure out crunches dont work. You need to burn the layer of fat over your abs threw intense cardio workouts. Such as skipping rope intensively and running. As you said already in your statement healthy eating is very much important in helping. make sure you lift weights also to encourage your body to build more muscle as a whole. I have a 6 pack got a six pack, experienced all that.

From what I understand you don't have any fat too lose, you just need to tone up. Not a problem! Crunches won't work alone, you need to work your back muscles as well, your entire body frankly. It should take a few weeks to a month to see real results. My source is a link to a list of really great workout dvds.

http://topexercisevideos.com/

You can do a million crunches a day, but if that's all you do it's not enough. Getting rid of the jiggly is a job for cardio exercise!

Dont have a time frame for you though, never went through that

Yes I think that if you wait about a few weeks cz I do 50-75 crunches and I can already feel results it's amazing but 100 you should feel results in a week