Can I withdrawl from medicare?

right now im a college sophmore 20 years old and have been working at albertsons for 6 months now. I noticed on my paystuvbs they deduct 5 dollars a week because of medicare. My coworker this old lady told me I should withdrawl because im only making about 100 a week and its not worth joining. am i able to withdrawl? and what is the medicare even for im only 20