[dāng nián]
（过去某一时间） in those years; in those days
This is the scalpel which Norman Bethune used in those days.
这是当年白求恩大夫用的手术刀。
Well, in those days there was no railway here.
想当年， 这里还没有火车呢!
He is as energetic as ever.
他的精力不减当年。
She is in her prime.
她正当年。