"What am I gonna do?" Jesse thought to himself. He looked more like a pre-pubescent 14 year old and not like his 18 year old stud of a self. Meanwhile his 13 year old brother almost looked old enough to drink! "It seems like Andy and I age when we are close together; all I gotta do is avoid him while I sort this out"
Right as Jesse finished that thought Andy burst into the kitchen, wearing Jesse's workout gear - a bro tank and shorts. "Wassup little bro. Let's go work out!" Andy cheered, his voice sounding an octave or two lower than before.
"How about no?" Jesse replied.
"Sorry bro, but I am responsible for you and I say we need to work out. You need to start building muscle while you are young if you wanna be huge like me." Andy said, flexing his muscles and shaking his crotch - you could see the bulge through the shorts.
"You're forgetting that I am still the older brother; you don't even have a driver's license or any experience driving. We're going back to that witch at the fair." Jesse said, feeling in control of the situation.
"Oh reeeeeally? Andy said as he stood over his brother. Being almost a foot and half taller make Andy look menacing to Jesse. Andy then pulled Jesse's head into a head lock and started tussling his hair. "You are such a joker little bro!" Andy teased as he held tight to Jesse. Jesse was too weak now to fight back and pull out of his brother's grip.
As the teasing continued Jesse felt that warm dizziness pass over him again. After a few seconds the sensation faded and Andy released Jesse. "WhaAt tHe hEll was thAT fOR!?" Jesse said, hearing his voice crack multiple times like a teenager's. Andy laughed with a new deep baritone of a voice, he looked like he was even taller now - 6 foot 4 now while Jesse was now a mere 5 foot 3. Andy now had a five o'clock shadow and thick hairy armpits. Jesse could even make out some chest hair creeping from the tank top his brother wore.
"Come on little bro, look." Andy pulled out his wallet which contained a driver's license in his name. "Let's go."
With that realization Jesse knew he was no longer the older brother - his younger brother was now an 18 year old according to the driver's license he now posessed. Jesse realized he was no longer in control - he was just the 13 year old younger brother to this stud of a man. Dejected, Jesse followed his brother out of the house and into what used to be his car.