Immediately after the stone glowed, Jon started to panic, as he felt himself getting smaller and smaller. Even his clothing was changing. "What's happening to me?" he asked aloud, hearing his voice getting less and less mature by the second.
When he finally stopped getting smaller, he looked at himself in his mirror and saw that he was younger, by about seven years. He was now Mikey's age.
It was at that moment that he realized what had happened. The stone made him switch ages with his little brother, so now Mikey (at age 17) was his older brother.
"This isn't what I wanted," he said, hearing his voice the way it sounded seven years ago. He reached into his pocket, but the stone wasn't there. Where did it go? He looked around the room, thinking he might have dropped it, but it was nowhere to be seen. One thing that caught his eye, however, was that this wasn't his bedroom. Yes, it looked similar, but little things (like photos and DVD's and a few posters) looked different.
And as Jon was still looking around at the changed room, the bedroom door opened and someone walked in.