It was nice, but I was still in high school so it didn't really feel like adulthood, that came in the form of my high school graduation, moving in to college, and then my 21st birthday.

Just enjoy it and appreciate the freedom and responsibility, but also take your time before acting on your newfound right to sign contracts. Maybe register to vote if you live in a democracy that doesn't do that automatically, for me that was the biggest thing about that age, I was finally a full citizen.