As a matter of fact, 30+ isn't really old when it comes to medical school. In my school 27-28 is the norm.
Second, you don't have to be a party star to be a good doctors. Those two types of personalities just don't connect. You don't have to smile and be social like a governor candidate to be a very competitive doctor.
As for your accent and immigration history (sorry, really can't find a better phrase), I definitely share your feelings. I came to US 7 years ago when I was in 10th grade for high school. I still have accent, and it's probably going to stay with me for the rest of my life. But here's a point.
I studied psychology in college. In psychology, there is a phenomenon called "the spotlight effect." It says "most of us really think other people pay more attention to us than they really do." For example, say you walk on street and you forget to zip your pants (you are a guy). You may think 90% of the people saw that but in fact only 5% saw you. So as non-US-born-Americans, we can be pretty sensitive to "whether people react especially positively to our actions." And it doesn't have to be that way. I used to have the same feelings. I felt like I had to dominate the conversation among 5 classmate to "prove" that I've mingled into my peers. It doesn't work like that. You can be quiet. You can just hold your drink and make some random comment every 5-10min. Look around your peers, I mean the "real Americans" (another bad phrase indeed). Many of them, if not majority of them are like this.
At last, you don't even have to be social. Who says you HAVE TO hang out with your classmates? I think everyone has his/her own support group. If that's only your spouse and kids, that's PERFECT!