You were eager to grow up too, so you rush towards the nearest bathroom. Brady tries to follow you, but given his new height, he has to force himself to walk slower since his strides are so much longer now. In the bathroom you and Brady go into the handicap stall. It's still early enough that only a few students have shown up to school so far. Nobody else should be walking in on you and your brother in the same bathroom stall. That would look weird enough without the magical pocket watch.
You take the watch from you pocket and hold it in your hand. 18 years old, you think to yourself. You can't wait to see how much you'll grow, given your clearly amazing genetics. You carefully move the knob just once. You still want to be in high school with Brady.
Almost instantly, your body convulses as you grow an inch or two. You start to fill out your baggy hoodie a bit more, but then your hoodie morphs into a basketball jersey. Even at 17 you're on varsity. Your jeans morph into basketball shorts, showing off your muscular, toned thighs. Your shoes transform into the same pair of Lebron's from Brady's car. Must be hand-me-downs from your big brother. Your hair becomes shaggier and messier as your face matures. A little bit of scruff appears on your face, a reasonable amount for a 17 year old. Best of all, you feel your own dick lengthen in the most orgasmic feeling you've ever had. Once the physical changes stop, new knowledge floods your brain: the ability to drive and play basketball. New memories fill in the spaces: winning the championship game last year with your brother, having college scouts looking at Brady and you. Memories of girlfriends and boyfriends, getting more blowjobs than you can even fathom. You are a very sexually active 17 year old.
Brady is watching the magic happen in awe. His brother is growing right before his eyes.
But you aren't done yet. You reach down and move the knob once more, aging you to 18. Again, your body convulses. You grow more in height, leaving you at about 6'4", taller than Brady. Your hair changes again to a middle part, as your face becomes even more mature. Your cheekbones and jawline become much more pronounced as even more hair grows on your face. At this point you have a pretty impressive amount of stubble. Going down, you now have chest hair poking out of your jersey. Reality changes your jersey to a t-shirt similar to Brady's. Your pecs and biceps push against it as your stomach clenches into a perfect 6-pack. The shorts you were wearing morph into a pair of joggers that are tight around your now even more muscular thighs. You can feel more hair growing on your legs down into the Lebrons, which change into a pair of Yeezys. Your dick lengthens even more, creating an incredibly noticeable bulge in your new joggers. You feel a sharp pain in your ears and reach up to realize that they're pierced now, which is nothing compared to the pain you feel on your forearm as you look down to learn that you now have a tattoo.
Just like before, more knowledge floods in. You and Brady are both 18 years old. You are fraternal twins, both blessed with immeasurable basketball skills. Despite being taller than Brady, you both wear the same size clothes, including size 12 shoes, which means that you and your brother trade clothes all the time. You'd both be graduating soon and scouts would be coming to your game this weekend to look at you for scholarships. You aren't in a relationship, but you have memories of several guys kneeling before you, struggling to take your massive cock in their mouths all at once. Thinking about these memories starts to make you hard.
You look over at Brady who is still standing in the corner of the stall. "How do you feel?" he asks.
"I feel," you stop when you hear how deep your voice is now. "I feel really amazing. And you remember everything too? Reality didn't affect you because you saw me change, right?"
"Yeah, I remember," Brady tells you.
You reach your hands up to feel your pecs, eager to see what else has changed about reality.