How do you understand if you're smart?

I'm 19

I can learn things easily if I sit and study, without much difficulty.
I think analytically(meaning that when there are real life situations in which I have to solve problems I consider them in a mathematical way).

I'm interested in learning a lot of things, differently from other people of my age that don't care much and prefer more "superficial" subjects.

When I talk with other people of my age i find it hard to find a connection with them because they often are like "yea bro look do you have something to smoke hehehe, bro I'm too high", or when someone talks about a concept that is more intellectual (philosophy/math/physics/history etc) they go like "yo what's that philosophical stuff", so I like talking only to a few friends, to the others I do small talk or just ask them questions because I like to have information about people like what's their job or what they want to do etc and since I know them see like what the more poor do compared to the richer or other type of stats.

Actually I rarely do this because I dont go out much, i just stay home and study and work out and stay with my gf or go out with her, and sometimes go out with some of my 5 friends.
I'm shit at social skills, until 2 years ago I had super social anxiety 0 friends and almost stuttered when talking to girl or other teenagers my age that I felt were intimidating.

All my teachers and my parents and my gf said that I'm smart (even if I was shit in high school because I didn't study).

Differently from other people I recognize my ignorance and want to learn instead of being convinced of knowing stuff and talking about it.

Maybe I'm just a normal intelligence guy but with different interests, and also an autist idk.

Ik those examples aren't that good
I'm not trying to "humble brag" or being like "I'm very smart", it's a genuine question that I'm curious about, how can i see how smart i am compared to others except by how I perceive me and them?