Can I exercise every day whenever I want to in order to lose weight?

Sure you can! It just won't help you lose much weight. Not 50 jumping jacks or some sit-ups or squats. That's not nearly enough to make a significant contribution to weight loss.

An hour of moderate cardio, or a half hour of intense cardio, five or more days per week can help you lose about a pound a week - if, and only if, you also manage your diet properly. A few minutes of calisthenics, a few times a day, won't even get you a tenth of that. It won't elevate your heart rate enough for long enough, and just doesn't burn enough calories to make a significant difference.

If you want to lose weight, you'll have to make a real commitment.

What are some good strength building exercise for teens?

I know where you're coming from, huge life change makes you want to redefine yourself.  Just make sure you're doing it for you.First, adolescence is when you start producing enough growth hormones to really start packing on muscle, and the stories about weightlifting stunting your growth have never been backed up in studies.

Do push ups get easier?

Yes, Push-ups get easier with time but they are must do even for the professional bodybuilders.If you are habitual of doing 50+ pushups daily at one go then with time you will find them easier to do and will become lesser effective as it won't take much effort. Therefore it is advised that after a month of this

Are six pack abs worth all the work to achieve?

Short answer no.For me, living in the UK it's always cold and miserable so I don't go to the beach often. The thing with 6 packs is they're (obviously )only visible with your shirt off. You gotta ask your self how many times your shirts gonna be off and