Back in the day he was the boxing champion of this area.
Tips
usage
想当年 opens reminiscing — typically a sentence about how things or people used to be, often with a touch of pride or nostalgia. It's the Chinese 'back in my day...' and like the English version it's a setup that signals an old-timer story is coming.
grammar
Sentence-initial only. 想当年 is a discourse opener; you don't drop it mid-clause. Pair it with 那时候 (nà shíhòu, 'at that time') or 当时 (dāngshí, 'then') to keep the reminiscence flowing.
