She's middle-aged.
她是中年人。
A Your mother is very young.
A 你的母亲很年轻。
B No, she's not. She's middle-aged!
B 不，她不年轻了。她人到中年了！
A Middle-aged? She's only about 40.
A 中年？她才大约40岁。
B 40 is middle-aged. 40 is old!
B 40岁是中年。40岁的人老了！
A 40 is not old! Wait till you're 40.
A 40并不老！等你到40岁看看就知道了。
B I never want to be middle-aged.
B 我永远也不想到中年。

Notes注释
1 Another way of describing people is by age. People can be young, / young, middle-aged / middle-aged, or old/ old. People don't see age in the same way, however: Your mother is very young./ Your mother is very young. / No, she's not. / No, she's not. / She's middle-aged. / She's middle-aged. / She's only about 40. / She's only about 40. / 40 is old. / 40 is old. / 40 is not old. / 40 is not old.
描述某个人的另一种方法是说他的年龄。人有年轻的, / young,中年的/ middle-aged,或者老年的/ old. 但是人们看年龄的方式不一样：Your mother is very young./ 你的母亲很年轻。/ No, she's not. /不，她不年轻了。/ She's middle-aged. /她人到中年了！/ She's only about 40. /她才大约40岁。/ 40 is old. /40岁的人老了！40 is not old. /40并不老！
2 Young people want to remain young: I never want to be middle-aged. / I never want to be middle-aged.
年轻人想保持年轻；I never want to be middle-aged. /我永远也不想到中年。

Key phrases and sentences
Your mother is very young.
No, she's not. She's middle-aged!
Middle-aged? She's only about 40.
40 is middle-aged. 40 is old!
40 is not old! Wait till you're 40.
I never want to be middle-aged.

你的母亲很年轻。
不，她不年轻了。她人到中年了！
中年？她才大约40岁。
40岁是中年。40岁的人老了！
40并不老！等你到40岁就知道了。
我永远也不想到中年。