I used to have no issues with narrower tires up until I finished college and went into the Navy - just a few days after my beloved Super Course with 25mm 700c tires was stolen. I used to push the tallest gear more often than not. I was also no more than a buck twenty five and n insanely good shape for cycling and running. The person riding bikes then is a very different person than who I am now. I have ridden on bikes where I have felt beaten up after the ride is done, and prefer to avoid that. I don't recall that sensation on anything wider than 25s, apart from one sloppy, rutted day on a cheap MTB on the C&O.
Yes, much depends on the bike and the ride. Some frames have limited clearance and 25s are the largest I'd attempt. However, when clearance is not an option, I tend to go large. I won't go smaller than 28s on those, but 32s or 35s are what I look for. This said, I have bikes with 42s and 54s, and those are sweet also. As long I don't feel like there's excess rolling resistance, and I'm not perpetually dealing with flats, I'm pretty easy.
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