At this age people are very stupid and at the same time most dangerous. I think you should avoid any discussion of religion with him and don't mention anything about your beliefs. Yes this young man can be very dangerous and do very evil things. Islam converts very normal people into beasts.
I agree with those who have said "keep an eye on your brother". You can never be "too careful".
If I were able to talk to your brother, I would say that the ONLY reason that he believes in Islam is that that is all he has known from the day he was born.
If your brother had been born in the mountains of New Guinea (to (say) the "Ooga-Booga" tribe, then he would swear black-and-blue that the **Ooga-Booga** religion was the "one true religion". ( That's a made-up tribe name, by the way..... ) WHY would he do that? Because he has been brainwashed (as all Muslims have been).
You are 19. Is it possible for you to move out, away from your brother? Maybe to a friend's place? That would give you a bit of "breathing space" to think about things. Bye for now - I'll try to keep an eye on how you're going..... Good luck! - enceladus
Undermining Islam - http://forum09.faithfreedom.org/viewtopic.php?f=10&t=15110