I managed to avoid getting baptized until I was 19. Had I been able to put it off a couple more years, when my doubts started to surface, I probably would have avoided it altogether. Unfortunately, there was an aggressive, utrazealous elder in my congregation who wouldn't let that happen.
My story is almost exactly the same, save the ultrazealous elder was my father. I made it to 19. After about 14 people just sorta assumed I was baptized, so it didn't really come up. What did it for me was my brother telling me at one point that he only got dunked because his friends were doing it, and that he felt like he'd done it for the wrong reasons. I resolved then and there that I'd only get baptized because I was sure about the religion and "loved jehovah."
Whenever someone pressured me to do it, I always came back with "This is a very important descision, and I don't want to do it for the wrong reasons. The more I'm pressured to do it, the more I instintively push back." Sometimes I would add something about them causing me to delay my baptism by pressuring me to do it. That always ended that, and I never got pushed by the same person twice, with the exception of my father.
I eventually broke my promise to myself and got baptized for the wrong reasons - I was heartbroken over a GF that had just broken up with me (she presumably assumed that I was already baptized) and my father knew just the right thing to say to take advantage of that, and somehow I was convinced it was all god calling me to the cult.
So, basically, if you can keep the kid from getting baptized because all their friends are doing it, then all you probably have to watch out for is when they're in an emotionally vulnerable situation. People only do things (this especially applies to joining a cult) if they think it's going to solve some problem for them. In my case, I essentially thought god was going to give me a girlfriend if I got baptized. Most kids don't want to be left out. Many just want the guilt-trips to end and don't realize that it's only the beginning of the guilt.