Why does my older brother act like this?

Hi. A little background before i explain my questions. My older brother is about 26. I work as a network engineer and he does Linux administration. Both of us graduated with a computer science degree. As the younger sibling I've always looked up to him, I mean who doesn't look up to the oldest sibling as the family pride and pillar. The issue is and i guess where my question comes from is why he acts or does the thing he does. He's great at his job and makes 90k annually being able to support himself in anyway, yet mentally he doesnt know how? he doesn't leave the house often other than work, and doesn't have many friends besides the ones i have. He's always anxious and asks too many questions for simple things like going to the store or getting invited to plans, almost like he's scared to come out. why do people ask so many questions to the point where they interrogate you every time you speak to them? He always feels like he needs his younger(16yr old) cousins to tell him what to do with everything. It feels like they're more in charge for his decisions than he is. Don't get me wrong they mean no hard but He doesn't take any lead or initiative on decision making, neither his or anyone else. You would think someone his age would move out, find a girlfriend, get married and start his own life. But instead he spends his time hanging out with 16 17yr olds. He's a successful kid, but it feels like he's easily tricked or persuaded into doing something, like he doesnt believe in himself at all. I dont understand where these characteristics or behaviors come from. Thanks for everything in advance