I am 19. I am still a JW, on the outside. Attend meetings, go out in service, give talks, etc... However, I am just going through the motions. I was raised in the "truth" and was baptized at 16, mostly due to pressure from a particular elder. My best friend (also a JW)began telling me a few things about the organization a few years ago, about the many inconsistencies and some of his doubts. At first, I would get so mad at him for telling me stuff. We got into more than one argument because I wanted him to shut up and stop making me doubt what I always knew as true, but he wouldn't. Today, I have him to thank for keeping the pressure on and making me realize what actually goes on.
What keeps me in now though is fear. Not so much fear of being shunned, but fear of hurting my dear friends and family. I know that once I get the courage to leave, I will be able to handle the shunning. I figure that true friendship is unconditional, and if I end up not having any true friends, so be it... I can make new ones. The problem I have is hurting my family, mostly. I am extremely close with my mother and aunt, and they would both be devastated if I left. My dad would be upset because he wants my mom to be happy, but since he himself is unactive I think I would be ok after a while with him.
So, ashi, to answer your question, overall I think it is fear and insecurity for me. I really care a lot of what others think of me, and don't want my image to be trashed. But, I guess I'll see in the long run what really happens.... I really am glad I finally started posting here. It helps a lot to talk to people who have similar feelings and experiences and doubts, and reassures me I'm not crazy.