Encourage him to join this forum. Perhaps after thinking back over his life first. That did it for me.
I'm 42. My ex first suggested that I had aspergers, maybe 6 years ago? I took online tests and scored highly, I tried to get a proper medical opinion but the NHS expert refused to commit (as adults are too good at compensating). I thought no more of it. But recently I started dating, and only then realized how different I am from NTs.
For all my life I've searched for somewhere that I really fit, and finally found this place, and I just feel at home for the first time. Encourage your brother to take a long hard look at his life, have a look at this site and think back to his childhood. See if he feels like he fits.