Is my brother autistic?

My brother is 26 and still lives at home. He's never really had any friends. He's really really quiet and shy when hes around people. Whenever were out somewhere without my mom, or if were at home and my moms not home, all he asks is Where's mom? What's she doing? When's she coming back? All he does is ask about he. It's like he's attached to her hip. He can't do anything on his own. Not to be mean, but he's not smart at all. He has absolutely no common sense. He studders A LOT. He can't even say one sentence without saying "um" or stopping. I had to use his phone one day because I broke mine and I wanted to check something on Facebook. He got notifications on his phone for this dating/porn website. That's none of my business but I thought it was disgusting. He hasn't had his first kiss yet, and I don't think he's ever had a girlfriend. I'm just really concerned about him. I never asked my nom about this because I know she'll be like YOU'RE SO RUDE WHY WOULD YOU ASK THAT. But in all seriousness, I just wana help him.