A:
At 58" tall his eyes should be at approximately 52" (the approximate center of the bowline). Using a 60" bow would leave 20+inches clearance to the ground plane.
He should be able to learn and grow into the 30# bow for some years to come before he'll want to switch limbs of a heavier weight. Ethically it is considered best to hunt with only 40# or heavier rated bow.