Im going through an existential crisis?

I maybe only 19 but time goes by fast but i feel worthless. Most of K-12 i was pretty mediocre and got grades just to get by and left high school last year with mostly C's in my accumulative (especially math and science) But when i look at my brother who's only 2yrs older got A and B's as long as i can remember in everything and got accepted into the University of Maryland , while i currently attend community college. And i wonder am i just not as smart as him? We grew up in the same house. What makes him so smart and successful and not me. I try to be motivated but sometimes i just don't understand some stuff. And i don't have many or any close friends, so he was even more successful than me socially.So basically the way i see it,compared to him to i'm boring idiot.