You can apply to schools that allow you to defer admission - a lot do this, usually for up to a year, sometimes two.
As for whether or not it’s worth doing a gap year in China - you need to have a plan for doing something other than just learning to speak the language better. Have you parents guided you on what they actually envision you doing, or given you any ideas about what you might do for a year? Just hanging out (anywhere) is a waste of a year. If you can intern, or volunteer, etc, and maybe do a bit of traveling, it might end up being a very worthwhile year. Alternatively, you can suggest to them that a gap year in China might make more sense after college, when you’re older, and can probably get more value out of it. (…even if you just do this to kick the can down the road…)