It's probably less common as you get older and leave college--semi-pro runners or local club racers in big cities in the US probably have older runners connected to the college kids and their resources...not common, but still possible.
On LRC here there was that 51-y/o dude who was ripped and ran a 2:55 on 50 mpw with killer recovery times.
In Columbus we have elite teams across Central Ohio but everyone seems to be clean.