How do I talk to a guy 2/3 years older than me?

I like him and we've never ever talked, he's in year 9 and I'm in year 7. My sister is in year 9 and she told me about him. My sister can't introduce me to him and she likes him a little. They're pretty close. She knows I like him. I want to start a conversation with him and I don't know how. He often sees me hanging out with my sister but I don't think he really cares. I just want to talk to him. (Extra info: I go to a British school.) What do I do??

Find out what he likes and hope to start a conversation with him.

honey stop, you're still too little, and at that age these kinds of age differences are pretty significant, he probably won't see you as his peer and only a child. Additionally, you said that your sister who's close with likes him too, do you really think that he is worth your relationship with her? Don't try to change yourself for a person