Age swap

I glared at him and then grinned, an idea coming to me. "Your wish was 'trade lives with Jonny' right?" I asked, toying with the stone. "Umm, yeah..." he replied hesitantly "...why?" "The exact wording was just to swap lives?" "Umm, yeah..." "Then I wish that I would become younger," I said "Ten years old to be exact, while you become older; seventeen exactly." Mikey's jaw dropped in shock, clearly not expecting me to have found that loophole.