Im a teenager and would like to tone up my body. I have a healthy diet, with lots of fruit and vegetables. I do 10-15 minutes of walking quickly a day, and have decided to start doing exercise on top of this. Im going to start running up and down the stairs for cardio, 200 squats and 200 stomach crunches (100 of those "reverse" crunches where you lift your knee close to your stomach and 100 regular crunches) a day. I also plan to start swimming on Sundays, for about 1-2 hours. I want to start push-ups after ive got into this regime. Will these regime, combined with a healthy diet, tone me up? How long will it be before I will see results?

Depends on your intensity level. Make sure to do some bw squats, and definitely pullups to keep your body balanced. Burpees and mountain climbers are good too.

You can do 200 squats?

ok.. first of all... are you a member of a gym?? its a lot easier and faster to see results. If you are, then make someone do your skinfold and girth measurements to see how much % of fat you have in your body and how is your weight in lean mass. A % of 20-25 is considered normal, however, if you want to tone up your body you would like to take that % down to 15% maintaining your lean mass or bringing it a little higher. So you should go ahead and get rid of that extra fat you have so you can work your muscles out. EAT EAT EAT!!! Thats the best way to get energy to work out. 6 meals a day will help you gain the energy you need and at the same time maintain your metabolism accelerated. Nutrition plays an important role in body toning or muscle building. Every 3 hrs you should have something to eat. Breakfast in the morning, ever forget to have your carb and protein. Your fruit of the day take it in the morning. Soy milk is good, is protein. Then a snack. Eventhough power bars work (power crunch cookie, protein plus ..etc), FOOD is the best way to feed your body. Always have your protein and carbs. Dont be afraid of eating bread , rice, potatoes, pasta etc... carbs are good they make you muscle grow, protein feed yor muscle.
Just make sure that the amount of carb is the amount you can get with your hand and teh protein should be as big as your hand palm.

THE WORK OUT!!!! Start doing lots of reps/ light weight. So your body get warmed. You will then see how your body responds and there is where you start putting more weight less reps to make the muscle bigger. Then you can vary. Some days less weight others light with lots of reps. Never stop when you think you cannot go more reps than 10. Do 3 more. There is where you bring you muscle to breaking tissues. Breaking tissues will lead to bigger muscle.

Dont be afraid of eating. JUST EAT HEALTHY!

(TIP) Look at the nutrition facts and be sure that the grams of sugar is 10% or less of the grams of carb. (TIP)

Do not work out every part of your body every day, and no more than three days a week. Start with either lower session or upper session (always working the mid session- im sure you want to have a 6 pack). So do upper body with abs one day, rest your body. Another day do lower body and abs.

DO CARDIO EVERYDAY. Run, or be part of an aeroics class. This will help you loose the fat while sweating.

Drink a gallon of water a day...

HOLY CRAP! If I did 200 squats I wouldn't be able to squat down to pee on the toilet the next day.....