2 years old, no foreskin-related problems. He did have one UTI as a baby, but it cleared right up with treatment. My friend's baby girl had a UTI, too, but no doctor in his right mind would have recommended circing her to prevent another one
My hubby is 37 (38 in July) and he has never had a problem.....nothing not even a UTI (and we've been together since 1989 so I know for sure for the past 21 years there has been absolutely nothing).
My 3.5y/o has no issues. We do nothing special.
Three boys, intact, no problems. My DS who is now 7 didn't retract until he was 6 and sometimes his foreskin was red and a little irritated, but it was only because it was "itchin' him" (lol) and he was fiddling with it all the time. Not a problem, in my book, but only natural.