Sorry just now haven't reply your qn about Mandarin.. then the
moment I remembered, my house's electricity went out 
(they were fixing my house lamp)
The Chinese at my dharma center are easy to understand. There
are English speaking people there also, whose Chinese isn't too
good. We don't use difficult technical terminologies to explain
things but ordinary, plain and simple Chinese.
In fact one of the local dharma teachers (english speaking and
holds a Ph.D) couldnt understand much Chinese, but my Master chose
him to teach the dharma (but he has left for Australia recently,
there's another Jen Chen Buddhist community there also). Can take
it as opportunity to learn Chinese also.. haha
As for age... there's adult class... youth class (teenagers) and
children class.
I'm still 18 but I go adult class more often... just a personal
choice since the time I came, like 13 years old (though their youth
class also quite fun).. or maybe my thinking very old