Not necessarily immaturity, but that you haven't had the same experience in life etc as most adults and have a lack of common ground on which to base a conversation. it can happen with people of the same age you've not much in common with, so is just as likely with an adult. some people don't feel comfortable making small talk, and there's only so far that can stretch anyway (ie after you've commented on a part of their outfit/appearance, the weather, where you are, what you've been up to, conversation can tend to dry up). It's also shyness as well, and you're probably shy and too self-aware to start talking about any old thing/random conversation because you don't want to look silly. it's something a lot of people suffer with. it doesn't mean you're an immature person, just that you're not naturally comfortable in conversations with people you don't know well. as you get older and have more experiences and meet people, you'll have a wider range of things and experiences to talk about and will probably lose the awkward feeling when talking to elders. don't worry about it, it's perfectly fine to sit and not make conversation at 100mph with a relative stranger, just be friendly and ask them questions and answer as fully as you can (i just mean more than "yeah" or "i dont mind really" which can often come out in place of what you really feel when you're shy). don't worry about it!x