Definition
to be very close to reaching a particular age, usually an older one
将近60、70等岁（通常指高齡）
He still looks young, but he's actually knocking on 60.
他看起来还很年轻，但实际上已经快60岁了。
My mother is knocking on 70, but she's still very active.
我母亲快70岁了，但她仍然非常活跃。
Although he's knocking on 80, he still goes for a walk every day.
虽然他快80岁了，但他仍然每天去散步。