Following on Lalit's note on young learner's ability to do text-based programming, I can share my experiences with young learners using block-based programming. I have found that when going beyond simple examples, the block diagrams can get difficult to read
It seems to me that block programming does not really scale from a comprehension point of view, and I think, hence, that it is good from a pedagogical point of view for young learners to get familiar with text-based programming as soon as possible, already
while taking the first steps in learning to read and type.
I have no "hard" empirical evidence on this, so it would be nice to find some academic research into the area of program comprehension and didactic wrt block- versus text-based programming. But my experience-based hypotheses are clearly in favor of text-based
(with good tool support, of course).