My teens (ages 13, 15 and 19) like to visit all the parks. The two girls (13 and 15 yo) still like the kiddie rides as well as the thrill rides. They'll ride the Pooh ride one minute and then be off on EE the next. My 19 yo ds sticks mostly to the thrill rides (TT, Space, TOT, RNR, BTMR, EE....). They also love the water parks, mini golf courses and shopping in DD. Renting watercraft is another favorite.
My ds does like to wander off on his own and will use disney transportation to get back and forth. Some days he just likes to chill at the resort or by the pool. With everyone having cell phones, it's so easy to keep in touch and meet up for meals etc.