Only younger or older guys flirt with me, why not boys my age?

It's possible you've made a bad impression on your own peer group. People who don't know you (younger people and older people) don't have any pre-established views of you, so they see you freshly. It's also possible you just appeal to different crowds. Sometimes the people in the grade below have WAY more in common with you than the people in your own grade, I know that from personal experience.