I want to ask out my best friends sister who's in a grade bellow me. What do I do?

so my best friends sister is really hot, and we both like each other. She comes to my friend and my water polo games and cheers us on. I'm in 8th grade an shes in 7th. Is it any eaisier asking someone out a grade bellow? And is it rigt for me to date my friends sister. And if we break up in the future I dont know how he'll react. What should I do?