I want a sixpack.

[Timo]

Doing sit ups everyday will have no affect if you have a layer of fat though. Note even skinny people have a layer of fat.
You need to lose fat and build muscle.
To lose fat do cardio workouts and lift weights. It can help to eat smaller dinners and maybe larger lunches.
Once the fat is gone you can do sit ups, crunches and whatever else.

My weight is 53 kilo (116.844 lb). I`m almost 14 y/o so is that good enough? I don't have like a belly or anything.