In the US there is no requirement that anyone take birth control. However if one is sexually active and does not want to get pregnant, or contract STDs, then taking birth control is the smart, responsible thing to do.
Nope. It's not mandatory to take birth control at a certain age. There are hundreds of reasons why a girl would need to begin birth control but it would be because a doctor felt it necessary. There are some very unique cases where a girl may never need birth control but again, a physician's diagnosis is always the best bet.