Is it normal that my 23 year old brother talks like a baby?

Ok so my brother is 23 and constantly talks like a baby, like when he's talking to people he acts like he's nine when he's not, and he doesn't do it on purpose. I think there's seriously something wrong with him like for instance if someone says something mean about him or something rude to him he doesn't say anything and just let's the person bash him. I know for a fact he was never bullied or abused so it has nothing to do with that. I'm not really describing it great but he acts immature but like a regular guy acts immature but like way way way over the top. Like once when my mom was in the hospital we kept going to see her, and the pricesss to see her would be like this: we go to the front desk get visitors passed go in the elevator to floor 3 go to front desk there ask to c mom in room 322 and they let u in. However when I went with my brother to visit my mom he was like "omg I'm so scared you do the talking" and I'm like what and he's like I don't know what to say, even though we'd been visiting my mom for a week now. He always says how scared he is to do normal things that aren't scary at all. Like calling to make an order on the phone. He's like this because he doesn't know how to talk like at all. He's unable to have a conversation for some reason without sounding like an idiot.