Same here buddy. I’m 30 and self teaching myself 2nd/3rd year undergrad math courses that I never learned since I wasn’t smart enough to pass the prereqs. I suppose like you I’m also considered competent at my job, but it’s not lost on me that people younger than me mastered this material a decade ago and are publishing cutting edge research. That’s just how it goes.

This past year I’ve had the misfortune of having an immediate family member suffer from a grave illness. It made me realize feeling bad about myself was just narcissism, and I need to continue to be my best but also spend less time feeling sorry for myself.

Best of luck to you in 2020 :)