Multiply your age by the number of megapixels and divide by the number of camera bodies you own.
I use 300, I think the default is actually 240, but it's pretty much irrelevant - the only thing it affects is the 100% size of the image when printing. If you use about 360dpi then the 100% size will be approximately A4. If you use "scale to fit page", then it's completely irrelevant.