If everyone re-reads the OP, she never stated that her old friends did not approve of her new friends, or that she had to choose between them. From other threads, Johnny has told us that she feels socially isolated, that she was dumped by others who she thought were her good friends, and that she is unhappy in HS and does not feel that she fits in. So finding good friends even if they are not in her grade is great for her. But she is worried that people in her grade are talking and this will make her fit in even less with her own classmates. Legitimate worry.
Johnny, I think it is worth the price. Good friends are so important, make all the difference. Age differences in friendships matter less as you get older and the gap is less meaningful. It looks like things might be improving for you, and I am happy to hear that. People talk, they will move on to something more interesting once they get used to the idea that you are friends with these girls. Don’t prevent the new friendship from doing things with your class when necessary, continue to be friendly with your own class, and I think they will forget about it and no longer think it is strange.