IF you are sitting long times in front of a computer you should make sure that your arms can rest on something. Your feet musnt hang at the edge of your chair. I'm 19 years old and I'm still using something under my leggs to not make them hang. The highest point of monitor should be below your eyes ~10 cm (~3,9 inc). Cutting down the internet is also a good choice :) but there is also offline games.. If my parents hadn't taken me to wrestling, football (european) or other sports I'dd prolly be fat too. I'm glad they did.