Is it normal that i feel inferior to people who are older than me?

It has nothing to do with the saying "Respect your elders"; it's just that I feel like if I am not the same age as someone I'm friends with, they'd see me or categorize me in their mind as "My Young Friend", and close by that category is "Cool Friends", who are their age. For instance, I know someone who is twenty-seven years old. I am eighteen years old, so there's a nine year difference, and every time I speak to this person I feel as though they are conversing with me to be nice, when in reality they can't wait to just get out of there and socialize with people their age or older. I feel like I should say something smart to get their attention, to make them see me as their equal, because people my own age don't click with me. (I am sure they are out there, but so far in real life I have had no luck). You may be thinking why I bother with these people if they make me feel this way, but it's not an outright thing. It's not as if they've simply blurted out, "Ugh, why am I speaking to you? You're so young!" to my face.

No matter how much alike they are to me, I feel that this age difference sets me apart in their eyes, as someone whose young and still hasn't seen as much as they have. What is it that they have seen that I haven't? I understand that as teenagers, we dislike the idea that we are not omniscient, but often I wonder how different their mind works at that age. Is it really as different and mature as they make themselves out to be, or does their ego just not accept befriending someone who seems inferior in knowledge and experience? To me I see it as a form of prejudice, how they don't seem to see you as human anymore when you don't show up on their radar as someone their age. Is it normal that I feel this way, that everyone I meet whose older than me by a few years is not ever going to see me as their equal?