It's a frightening thought, but feet grow after the age of 20. I've subconsciously wondered for about a year or so, why my 9.5 size shoes (and even one size 10 pair) feel painfully snug, only to find out that my feet are hovering somewhere around 10.5. This happened as I was finally caming to terms with being a size 9.5... I really don't care how big my feet look, the only problem is it's really hard to find shoes after you pass the 10.0 mark. I've searched everywhere for cute boots or booties with a medium heel (about 2.5 inches) and have been unable to find anything for under 100 dollars.
Another frightening fact: my sister's feet grew one size after the birth of her son, our friend Kelly's feet grew a half size with each child (she has three). If I want to have a couple of kids (which I do), my feet will be around 11 to 12.... OMG I'll have to have custom-made shoes, I guess...
And god knows what happens to shoe size after middle age! I mean, it's clear that anything with a cartilage in it grows (nose, ears), while everything else (height, amount of hair) shrinks. If feet do grow, and, keeping in mind my ...khem... prominent nose and more than moderately-sized ears, I should look something like the following picture in a couple of decades, minus the blue adorable-ness, of course :)))