My question is, should I take a class that is more than once a week and have tutors?Kai-Tea: Yes, certainly. Well, maybe. If your goal is to become a translator in 6 years or so, you should absolutely be studying at least 2-3 hours a day, 7 days a week. Not necessarily in a class or with a tutor, though, since self-study can also be very effective and certainly very economical. Building even a decent fluency takes a lot of time and effort, no matter what your age is.
Similarly, Jenny, I think that your problems with listening and speaking Chinese have more to do with the large difference between Chinese and English, and less with not having started studying it seriously before 20. Studying on and off for 5 years and then 2 years abroad isn't really that much when it comes to languages not in the same language family with your mother tongue.
The research doesn't disagree that there is a golden age of language learning, but that ends already at 3-15 (depending on which study you look at), and that your overall mental skills start to deteriorate at your early twenties. Yet, there are plenty of people who've built excellent language skills at adult age, and even learning your mother tongue as a kid wasn't that easy. Just think about how long it took until you could properly write and speak the refined "adult language"...
Another way to think about it is to ask yourself if you would've just given up on everything if you were born 10% less smart. So why give up now even if you've lost some of your mental resources to age? Just put in a bit more effort. Also, exercising your mind with language learning (or any learning activity) will slow down the aging process so there's a double benefit.