Jim grew older, as the balloon inflated more and more and more.
He grew to 18... to 20... to 25... to 28, and kept on growing older till he was roughly around 32 years old - a grownup man.
He glanced at his reflection in the mirror.
His kid self's clothing looked rather split and ragged; the shirt was reduced to a tattered looking waistcoat, and his shorts no longer reached his knees and looked ragged on the hems, almost similar to that of the Incredible Hulk.
He saw that he was now 5'11". As tall as his dad and the height that the old man made him when he demonstrated the balloon to him.
He found his brown hair looked rather shaggy, and he'd also gained a trucker-style beard. And he had some muscle on him.
"Wow." He said, in a deep, gruff, voice. "This must be what it's like to be grown up, and what I'm gonna look like as a grownup. "
He wriggled his grownup toes.
He thought of bringing himself back to normal.
But first, he thought of wanting to experience his new grownup look.
He also wondered if the balloon could inflate his grownup body.