There are many gifted adults in medical profession. Gifted with social issue (2E) such as Asperger tend to stay in science and academic/research setting. (a lot of PhDs and not many MDs) When he starts doing research, he will see some PhDs in the research field just like him. I am sure he knows he is different and he should know that he has something special to contribute to this world and people will accept for who he is.

Please let him now that Graduate school is different than High School or Middle School. Keep open minded and the doors that he never thought existed will open for him.

Good luck!