I feel this, imposter syndrome is massive atm. Especially since my new boss wants me to be put into a leadership role and I'm like "UHHHHH I AM STILL A BABY!" (let's ignore the fact that I am turning 28 in a week...). I'll get there with you, slowly. But eventually.
I know exactly what you mean, I'm 33 and I still feel like I'm still a baby. Haha. Sometimes it's best to just absolutely fake it till you make it, or rather fake believing in yourself so well that at some point, you do believe in yourself.