I'm Anglican, and the whole baptism/confirmation thing that DanTheMan mentioned applies for me, too. Anglicans are baptized as infants, and then, when we're about 12 years old or so, we get confirmed in the Anglican Church and then we can receive Holy Communion. Like DanTheMan said, it's like a reaffirmation of your faith and membership in the Church, a renewal of your baptismal vows that your parents and god-parents took for you as an infant, and it's sort of a big thing. I remember when I was confirmed, all of my family got together for the church service, then we had a big family dinner and there was lots of picture-taking and all of that, it was a good day, white dress notwithstanding.
Of course, maybe 12 years old is kinda young to become a full-fledged member of a church, but in my church, there are no demands made of confirmed members, no restrictions and certainly no threats. I don't go to church very often and the only person that bugs me about it is my grandmother. And if I decide to convert or just not bother ever going to church ever again, nobody's gonna be angry with me, I won't lose my family, I won't be booted out of my church because I don't attend and believe anymore. As a matter of fact, if I left and then went back, they'd welcome me with open arms, no questions, just like they welcome anyone who wants to attend the services and understand when someone doesn't want to attend anymore. And really, confirmation isn't necessary - it's sort of expected, but you don't have to do it if you don't want to, or you can wait until you're older. When I was confirmed, one of my fellow confirmation students (we had to take some "confirmation classes" before the actual confirmation, kinda like Sunday school) was confirmed with his father, who was much older and had never been confirmed. Just goes to show the kind of religious freedom we mainstream-Christians have.
It's a beautiful thing, not being bound by strict rules and regulations. I have my faith, I know what I believe, but I don't feel compelled to attend church services on a regular basis, I don't have anyone nagging me about it, I don't have to go knocking on other people's doors to bug them about my beliefs and I don't have to worry about losing my whole life if my beliefs ever change.
For JWs, I don't think anyone under 21, or even 19, should be allowed to get baptized. If you're not old enough to drink legally (21 in the US, 19 here in Canada), then you're damn well not old enough to sell your soul to these people and put your entire personal life on the line for a bunch of old men in Brooklyn. Until you're old enough to go out and get plastered at the bar with your buddies, you shouldn't be allowed to make decisions that affect your life like baptism into the WTS affects your life.
Just an opinion.