I returned to Cortland, NY to visit a friend of mine. While I was there, I was able to talk with my Professional Writing professors, who invited me to sit in on their classes. It was an absolute blast. It was such a rush being back in my old stomping grounds, talking about my the subject I love, and since the first class was Revising and Editing, and they were discussing punctuation, it was even focused on my specialty.
What really struck me, though, was that I knew everything there. Now, I've always been good at grammar and syntax, but it is not an easy subject. If you aren't very dedicated to studying it, it will take you a while to pick up the nuances of using colons, semicolons, dashes, and parenthetical commas (the specific subject of that day). But that day, it took all my strength not to just blurt out every answer when the teacher asked a question.
And that was when I realized how far I've come. It's not just that I know how to use punctuation, it's that I know why to use it (to the degree that one even can understand why anything is done in our crazy language). And more than that, I know it for certain; I'm not guessing.
When I was taking that class for credit so many years ago, I did not know how to use dashes. If I was asked how a colon works, I would have to search my head to find the words to explain it. But now, I can just spout the answers as a reflex.
Look back at your own past. If you can, try to return to places or scenes that used to be common stomping grounds. If they haven't changed, then use them as a point of reference for how much you have. It is a wonderful boost of confidence to see how far you've come.