There are several resident gurus on S-B roller mowers. At least one of them - probably Deejay - is bound to respond to your questions shortly.

Some of the parts for those mowers are readily available and some are not. So far as the dented front roller is concerned, it depends mostly on whether the roller is deformed, so the mower bumps up and down when you roll it along a smooth surface: this could make it mow the lawn in bumpy fashion also.

Your rotating blade (cylinder) seems to have seldom if ever been resharpened, which means there is plenty of meat on it for future sharpening. This is a good thing, since they are expensive to replace. The rust on the outermost surface of the cylinder seems well-established, which does not entirely match the claim that it was sharpened and adjusted only two months ago. However I have not seen the mower itself, and am not accusing the seller of misleading you.

As you said, the mower has some cosmetic deterioration and you have to expect this at its age, but externally it looks rather good. I'll leave the dating to Deejay - he can make an estimate from the serial number, though I do not think specific data exist. However if you look at the cooling air cowl on the Briggs and Stratton engine, you will find a very long series of numbers stamped on it. If you post that series of numbers we can tell you the year and month the engine was manufactured. If it is the original engine you will then know the approximate build date of the mower.