At 17, I promised my cat I'd marry him if I wasn't married by 27. The summer I turned 26(my birthday is in September), I started picking out rings to fit a cat. In July, I met an obnoxious man that wouldn't stop badgering me. I married him shy of two weeks to 27. So, life changed a lot about that time.
For me, the 30s has been relatively awesome. The hormones start to calm a bit, and you can start reflecting what you want life to be like. The best advice I can give is question everything. See how much of what you do/say/think/'feel/enjoy is you, and how much is programmed from culture, friends, or upbringing.
Experience. That doesn't mean you have to go to Timbuktu, you can experience new things right where you are. Look around where you live. Get familiar with it. Investigate stores or restaurants you haven't been to. Check out any natural areas nearby. Get to know your landscape.
Learn to be okay with aging. No, you're far from old, but as I near 40, and my 'people' go through their 30s, I'm seeing those that are okay with aging and don't take it as a personal reflection, and don't try to cling madly to what once was end up relatively level, and those that do are constantly upset, wishing, pining for something now gone.
And of course, enjoy the ride.