Most people learning programming have already been exposed to function calling in math (f(x)=x+1). Recursion is not a very big jump semantically from this. Conditional loops are a (relatively) big jump.
I'd be very shocked if anyone past the age of 4 or 5 had never heard (and learned to understand) statements like "Wash your hands until they're clean" which is a conditional loop (wash your hands, check if they're still dirty, repeat if they are, stop otherwise). If a teen or adult learning to program has trouble with conditional loops, I'd be very very surprised. The translation into programming languages (syntax) may be a challenge, the correct logical expressions for their intent may be a challenge, but the concept should not be.
I happen to know (due to job), that many adults have problems grasping for loops (in Python) when learning programming. It is one of the main points where problems arise in programming introductions.
It may all depend on how it is explained for what person, as different people understand different explanations better than others. Or it may be syntax related. Or that people for the first time fathom how they can make the computer do things in such a time saving manner. Who knows.
