My younger sister already has a boyfriend?

She's only 12 (turning 13 this september) and im 15. Its not about the jelousy thing ( cause i havent gotten a guy yet and HAVE no plans on getting one )but im kinda worried for her. You know...ugh but she looks mature enough for her age. (like she acts more teeny than me) her friends and my cousin who always talk about lovey dovey stuff.. The main point is SHE 'S TOO YOUNG i think :/ and my parents obviously didnt know...Please help?