"How about going for a swim? It's a pool party, after all."
Chris seemed to like that idea, and nodded, grinning at his brother. You both had to get changed, though, so you went inside first. You may be brothers, but changing in the same room is pretty weird at this age.
A minute or two after you finished changing, Chris stepped out of the bathroom as well.
"Woah" You said subconsciously.
Chris looked a lot different than he did before. Along with the height increase, he looked a good bit more toned than he did. He wasn't really 'muscular' now, but he certainly wasn't the weak little kid he was a month ago. His stomach was flatter, and his arms had more width to them. His pecs also seemed slightly more outlined than they did before. He could probably beat up a lot of other kids his age, you thought.
Not only did he seem to he more muscular, you couldn't help but notice how he changed in other areas. His chest was dusted by blond-brown hair, connected to a very dark and noticeable happy trail. When he lifted his arm to adjust his hair, you also saw thick, full bushes of armpit hair that were certainly not there before.
And looking further down... Well, you didn't want to look at your brother down 'there',, but it was worth noting. He seemed to bulge out slightly around his crotch, something you know for a fact was not there before. You didn't worry about him possibly being bigger than you or anything like that, though. You had a pretty big size of 7 inches while flaccid, and you could see you bulged a good bit more than Chris.
"Eyes up here, big bro." Chris grinned at you again, and you guiltily adjusted your stare. The sound startled you, still not used to his deeper voice. It was nowhere near yours, and still had a kid-like ring to it, but it was a drastic change from a month ago. It would get even deeper soon, you thought.
Looking at his face, it also seemed much more mature than before. Less round, more of a jawline. You thought you even saw a wispy peach fuzz mustache.
As you climbed into the pool, you thought about what the hell could be going on. He claims he's a "lucky quick bloomer", but this seems like too absurd for that. It's only been a month! He's still short for his age, at about 5'2 now, but that is still a foot of growth in a month! Not to mention the hair. He's only 13, for God's sakes.
Chris didn't waste any time like you did, and cannonballed into the pool from the deep end, sending a massive splash of water over Nate.
You sputter a bit, and wipe your eyes. When you look back, Chris surfaced in front of you.
"Hey big bro, I bet I can swim faster than you now! Wanna race to the other side?"