"Hi guys!" Matthew greeted his little brothers as he entered the house. He didn't live there but he usually visited his parents' home when he has a break.
Jim heard his brother's voice and he thought it was a perfect opportunity to test his balloon on him. Matthew was his favorite brother and he admired him a lot. Also, he had just turned 22 which it's the coolest age to do grown-up's stuff, according to what Matthew has told him.
"Hey, Matt!!" Jim called for his brother without leaving his room. "Come here!!" A brief moment later, Matthew was in there.
"What's up, Jim?!" Matthew smiled and showed his perfect teeth and lovely pimples. Of course, he's very athletic, tall and well-built. His brown curly hair looked gorgeous and he has the right amount of body hair to look manly but not too much. In other words, his handsomeness was completely stunning.
"I want to show you something unbelievable, but you must keep it as a secret." Jim said before he showed him the balloon he was hiding behind his back. "I got it this morning and it's kind of magic!"
"Magic?!" Matthew laughed. "It's some kind of joke?"
"No, I can demonstrate it but you must keep discretion. Promise?" Matthew nodded although he didn't seem convinced. "Ok, control my age and muscles!"
Jim blew once and immediately he started to grow bigger in every way possible. His small frame got some weight and a few dark hairs started to sprout in his exposed legs. He didn't get as old as Matthew but he was definitely older.
"No fucking way!!" Matthew was open-mouthed. "You are older!! You look like Isaac!!"
"I guess I'm 17, now." Jim replied and his deeper voice astounded his brother a little. "It's funny to see you almost eye to eye."
"So... if that thing can change your age..." Matthew was saying. "Can you become my age? I always wanted a twin brother like Wyatt and David or Walt and Cal."
"Twin brother?" Jim smiled at the idea. "That sounds cool but I can't exactly control how old I grow."
"Mmm.." Matthew was thinking until he got an idea. "Use this!" He took off his left shoe and gave it to Jim. "If you're going to be my twin brother we must have the same shoe size, I'm size 15 by the way."
"15?! It's twice my shoe size!!" Jim shouted.
"Well, big feet is on the family. Look." Matthew pointed at Jim's feet and they looked quite big already. "You're not too far from size 15."
Jim blushed for a moment before he put his feet on Matthew's left shoe. It smelled a little bad and Jim felt a little embarrassed that his feet could smell like that. He wiggled his toes inside the shoe before he used the balloon again. "Control my age and muscles." He blew once and he felt his soles moving through the shoe but it wasn't enough. He did it twice again until he felt some constriction, he released some air until he felt it comfortable. He stared at his right foot, they were way more bigger and hairier than his 12 years old self.
"Wow, shiiit!!" Matthew shouted. "It's like looking into a mirror!!"
"Don't shout or someone could hear you!" Jim told him and immediately he got astounded by his own voice.
"You even sound like me!" Matthew grinned before he started to look on detail at his new twin brother. "Tall, well-built, maybe a little bit hairier... you're fine but I need see one thing before I say you're as good looking as me."
He suddenly and unexpectedly tore off Jim's tight shorts and boxers that barely held themselves around Jim's bigger waist and legs. A big long uncut dick covered in sweat and precum jumped out to life like Keiko in the Free Willy movie. Jim felt ashamed of being exposed to his brother, but Matthew looked quite normal.
"Good good!" Matthew said while he inspected his brother's dick. Touching everywhere, feeling its weight and thickness. Then he held his balls and even he took out some pubes. "What do you say if we compare?"
"C-compare?" Jim hesitated as he saw his brother, his role model, taking off his pants and boxers to reveal his own schlong. "Damn, it's huge!" Jim absent-mindedly said.
"I know right." Matthew grinned. "And it seems that not just big feet run on the family." He began to stroke his dick and Jim's one too and he did it for a while until Jim's blew out his first load. He lasted a little bit more until they both were covered in their cums.
"It was my first time." Jim panted quite ashamed. He didn't expect this was going to happen when he showed the balloon to his brother.
"The first from many." Matthew grinned. "You can't go back to be a kid! You must come back to college with me!"
"Wait, what?!!"
"I'll talk with mom and dad, and you can get a job close to the university!" Matthew was speaking so fast that Jim can't reply him. "You don't have clothes but don't worry, I have some extra in my bag..." He stopped talking for a moment before he grinned again. "I have another idea."
Matthew ran out of the room while Jim was still getting used to his bigger body. He rubbed at the hair that had grown under his armpits, the stubble on his face and the hair that had sprouted from his nipples to the thick bush above his swollen dick. "I had a different idea about growing up."
"Here!" Matthew shouted at Jim while he was down the door frame. "Put this on and use your magic balloon again!" Jim looked at the clothes that his brother had gave him. It's his father's clothes! "Now, we both will grow to dad's age!!"