If you cannot get the KSC because you cannot rent a car due to your age, I suggest trying the tour companies that will have limited space available.
http://www.grayline.com/Grayline/des...1&itemcount=7&
If you can manage to find a car, you may purchase your tickets from the KSC website when they become available. This site also has directions on getting to the center.
http://www.kennedyspacecenter.com/
BE FOREWARNED!!!
Launch scrubs are very frequent either due to glitches with the shuttle or because our Florida weather will not cooperate (especially in the summer). I have been to the center 3 times for launches and was only able to see the shuttle launch once.