Jim came to a halt in the main thoroughfare of the mall, his mind still reeling with the possibilities of the balloon. There were a number of scores he wanted to settle, but the first thing his mind turned to was self-improvement. At 12 years old, Jim was beginning to notice the teenage girls who flounced through the mall, and wanted them to notice him. But in his current state, even with the extra inch or so he'd be left with at the end of the old man's demonstration, there was no chance of that - he was a small, skinny preteen.
But I can fix that, he thought, holding the red balloon.
"Control my manliness," he said, hoping it would work. He drew a deep breath and blew into the balloon. Immediately he felt the stretching sensation again, but this time it was different. His shirt tightened again, but this time it was focused at the shoulders and chest; his jeans began to pinch at the hips. Looking in the window of a nearby shop he saw a taller and more athletic 12 year old, well built for his age and rapidly becoming more so. He ran out of puff as he crossed the threshold for a serious athlete and held the balloon shut with his thumb.
"Wow." As he had simply said manliness, the balloon had not simply made him older, it had boosted his testosterone levels. He was almost six feet tall, shirt riding up to expose a nice six-pack of ab muscles and generous pecs. His jeans strained to contain his legs. He looked almost freakishly big, like he was a serious athlete, maybe a football player. His package looked almost obscene; zip clearly about to give way under an endowment far in excess of the boy-junk he'd sported that morning.
"Release," he said, then cautiously allowed air to flow out of the balloon. His gains remained. Awesome.