As the now-tall boy walked off, Jim looked for another victim. But then he had a lightbulb moment - he could change himself! But what to change?
Jim realized he could do the same thing as he did to the other boy, but since it was himself, he wouldn't have to worry about memory or the public. He ducked behind a shelf and whispered "control my size" to the balloon.
However before he started, he reconsidered. Unlike the boy, he wanted to be older as well. So he said "control my size and age" to the balloon. There, that should do it, he thought. He drew a deep breath and blew into the balloon.
Immediately he felt a stretching sensation. His shirt tightened, particularly at the shoulders and chest, and his jeans began to pinch at the hips. Looking in the mirror, he saw a 14 - no, 15-year-old boy blowing into a balloon; well built for his age and rapidly becoming more so. He ran out of puff as he crossed the 16-year threshold and held the balloon shut with his thumb.
"Wow." As he had paired age with size, the balloon had not simply made him older, it had made him disproportionately taller and muscular than he would have otherwise been at this age. At 16, he was just over six feet tall, shirt riding up to expose a nice four-pack of ab muscles and tight across generous pecs. His jeans, now mid-calf, strained to contain his legs; he didn't look freakishly big, but he definitely looked like he was a serious athlete; maybe a swimmer. His package looked bigger as well, with a slight bulge in his jeans. He wondered if it too had been enhanced further, or if a big dick was in his future anyway. In fact... "release" Jim said and then looked down, "control the size of my cock". He blew one big breath into the balloon and watched as the bulge in his jeans swelled up just that much. Perfect, he thought. "Release"