As soon as his mother was dead, he had begun to grow. All the growth spurts of adolescence through which he had crept, barely keeping up with the minimum standards of height and heft for his age, had come upon him suddenly, and his bones had built and built themselves at crazy speeds, dragging at the muscles until he feared a little for his ligature, and almost ran, when he ran, just a little carefully, he who had decided never to be careful again.
The bones had grown, and muscles had stretched with steady effort over them, and within ten months he was nearly two meters tall, and his shoulders were broad, and his voice was not merely deep but rolled from a heavy chest, and only his skin suggested porcelain.
And of course his rational mind knew, the mind that was studying for medical-school exams, that his body was not growing because his mother was no more.
But he knew that it really was. He had only been waiting on her word, all these years, and having left the world she had given him leave to leave her. He was a man, and whatever he might become, he would never again be anyone's doll.
(Because in both instances where we see him, younger Kazutaka in the manga is nearly a dead ringer for Hisoka, and the 'would you cry for me' Oriya flashback was apparently during college.)