It takes time… I was one of the middle schoolers who got hooked on juul and kept vaping till my junior year of high school. Unfortunately, I still use zyn (which isn’t as bad) but it beats not being able to breathe. It took years for me to get back to 100% but it’s possible. My advice is to take it slow while still pushing yourself daily and only compare yourself to your past… I’m still relatively slow (avg 9:14/m pace for 6 miles) but I celebrate that I’m better than I was. Wishing u luck!