For what its worth, I never train my calves..
Last I measured, they were at 17.5". Nothing quite as impressive as other individuals mentioned in this thread, just anecdotal experience.
I also spoke with Mr. @Tim_Patterson about calves at one point and he had mentioned that some people are genetically blessed with calves, and others have to train them hard. I believe he mentioned training an individual with great calves (genetically) and after training calves hard for some time, they looked worse.
In short: Some people need to train calves, others would be fine (or better) if they didn’t.
Just my 2 cents.