How do I get over my 'knowledge' insecurity?

I'm 16 and I'm still pretty dumb. Ever since I was 14 I've had this insecurity, it's one of my biggest flaws and it's one of the most or even the most esteem killing insecurities I have.

I do love to learn and I would really like to know about everything but I find it hard, I know at my age it's reasonable to not be interested into certain things or be able to understand certain things but I've found that in class discussions sometimes, I get very anxious for myself because some kids know a lottt. When I hear their opinions I can agree to it or disagree and think for myself but sometimes if it's more a complex discussion, I can agree or disagree but it's a very weak one without any reasoning, it's more instinctive.

I typically shut up if I don't know anything about a subject and I listen to people. I surround myself with people whose knowledgeablities and reasoning are significantly higher than mine. Like people who challenge me in some way.

Whenever I'm 'overpowered' on a topic I feel a sense of defeat. I do have my own skills that many people wish to have, but these are more practical/applicable skills but it doesn't feed my common sense since they're pretty much the only things I do but I try to combine them sometimes.. but I'm way more passionate about what I do myself than what's beyond my bubble and I don't like it.

I'm usually open to opinions and experiences and stuff but I find myself at times avoiding discussions or asking questions out of fear (this is improving a lot but it's still kinda there..)

I really don't want to come across as stupid when I'm in my 20s, I have a hard time concentrating on nearly anything I read. I do take notes sometimes..

Any advice? Can you relate? If anyone had this insecurity can you tell me how you got over it??