I'm 25, running 50 miles per week for the last year, no injuries or interruptions. In 2009 I ran 60-80 miles per week, around 100 for a month in the summer of 2010 and 50-70 throughout 2011.
2003-2011 I was size 12 in everything. In early 2012 I sized down to 11.5 in trainers but kept 12s in flats and spikes. Now I'm 11.5 in everything and got my first-ever pair of narrow width trainers this week in 11.5 B. In Brooks PureFlow2 I can even wear an 11 comfortably.
I've noticed my casual shoes size shrink too. In dress shoes I can now wear 11 when before I wore 11.5 for years. I even have a pair of western boots (I'm from Texas) in 10.5!
Question stands: can feet shrink with age or mileage? I'm not logging very high mileage but I run 6-7 days a week, every week.