After thinking a moment, the obvious choice came up again. His penis. He would grow his penis.
He dropped his pants and pulled down his underwear. There it was, looking somewhat small and mostly hairless. Two inches. It was the reason he hated taking showers in public. Most other boys his age were more developed than him. They had lots of hair. Jim just felt embarrassed by how immature he looked in comparison.
He looked at himself in the mirror, "Are you really ready to do this?" he asked himself. He hesitated a moment. "Yeah. Yeah, let's do it."
Jim took a breath to steady his nerves. "Control my penis age," he said.
Suddenly, he drew a quick, deep breath and blew into the balloon. "FFOOOOOOOOFFF."
Hair sprouted around his genitals. His small penis thickened and grew a full two inches longer as his balls swelled and drooped. Jim smiled.
Again, he blew into the balloon. "FFFOOOOOOOOOOOFF." And again his penis grew even more mature. He now had the penis of an older high school student. It looked humorously incongruous on his thin, boyish body, but Jim didn't care. Jim had a penis to be proud of now, 5 inches soft and thick as a toothpaste tube.
"Awesome!" he said.
Somewhere in his mind, he considered stopping. It would be the reasonable thing to do. There was no good reason to go any further. Yet in spite of that, he found himself lifting the balloon to his lips again and taking a deep breath. He couldn't stop now. The power was intoxicating, addicting. He needed more.
He blew, and the balloon expanded. "FFFFOOOOOOOOOFFF." He now had the penis of a full grown adult, 7 inches soft and surrounded by a thick bush of pubes.
Not bad for a 12 year old, he thought.
Jim smiled.
"Release," he said. He let the air loose from the balloon as he stared at his transformed crotch. It was an awe inspiring sight. Suddenly, his penis had become as large as he had yearned for it to be, and yet he couldn't shake the feeling that it was an alien addition to his body. For sure, it was his, but it didn't feel like it belonged to him. It felt like he was borrowing something from an older version of himself.
Hesitantly, Jim lifted his right hand and grasped his massive member. It felt heavy and warm in his boyish hand. He gently ran his small hand down its length. "Wow," he said, amazed by the stimulating sensation of handling his sensitive adult dick.
Who cares if it doesn't feel like mine, he thought. It feels so good, and anyways, it's mine for now.
"What am I going to do with you?" he asked as he stared at his manhood and smiled.