I really need help...parent troubles

I have been seeing this guy let’s call him T for almost 7 months. My parents completely refuse to let me and him be together despite the fact that I am 18. The biggest issue they have is that he is 21. T is the sweetest guy I know and we just click. I am definitely falling for him and I don’t know how to tell my parents at this point. I need suggestions on how to ease them in or convince them to get to know him...I just can’t let him go.