Not many years ago, I worked outside of the UK.

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In this sentence, what other expressions can we use in place of 'not many years ago'? Is it 'a few days ago'?

"A few days" is more specific and seemingly much shorter than "years." How about "recently," "not long ago," "a while ago?"

some years ago

In place of "not many years ago," you can use several expressions to convey a similar meaning. One option could be "a short while ago" or "some time back." Another possibility is "not too long ago" or "recently." These phrases indicate a period of time that is not a significant number of years but still denotes a past occurrence.

Regarding your second question, "a few days ago" specifically refers to a short period of time, typically within the past week. It doesn't carry the same meaning as "not many years ago," which generally implies a more substantial timeframe. So, while "a few days ago" can be a suitable replacement in certain situations, it may not accurately convey the intended message in this context.