I guess it depends on where you come from. Like I don't remember anything special about turning sixteen back home, but there's ceremonies and festivals and stuff for other milestones. There's Shichi-Go-San for kids, the Coming of Age day for people who just turned twenty... and some others, too, though not all of them are practiced nowadays.

[shakes her head]

Sorry, I didn't mean to ramble on like that. Anyway, I guess what I'm trying to say is that it's all a part of growing up, and getting one step closer to being an actual adult. Maybe that's what they're celebrating when somebody turns sixteen.