I just wat to go on a date with a older guy?

I am a freshmen in highschool and I meet this guy who is a junior. I met him through my friend (its her cousin) however my mom does not approve of this friend. However I have been talking to her cousin and hes pretty cool. He asked me out but I cant go anywhere because my mom thinks he is too old! What can I do to convince her? I get really good grades and in all honors classes. Including a weighted grade class. I have all As & Bs!