I NEED ADVICE

so recently I’ve been lowkey flirting with this junior + I’m a freshmen, but a lot of people have been coming at me lately for wanting to be with him or even hanging out with him. They say that he’s too old but I’m 15 and he’s 17-18. Is he too old . I mean, I guess it makes since, because he is more mature than me but still I would at least wanna be friends with him. What do I do? And if I shouldn’t be with him, how do I tell him?