would imagine, say, think, etc. (that)… used to give opinions that you are not certain about
I would imagine the job will take about two days.
I'd say he was about fifty.
My question is that does "I'd say he was about fifty."="he could be about fifty." & "I would imagine the job will take about two days."="The job could take about two days"?
Second, do you native say "I would say he could be about fifty."? (I am not sure whether we should use "could" in "he could be about fifty." or "could" is unnecessary.) I would think that way of saying is not idiomatic, but I am not sure.