Judy eventually buys it

"Judy! It's me! John!"
"What are you trying to pull? You are obviously not, bitch!" yelled Judy as she was dialing. John's brain started to work harder, since Judy wasn't going to take his word for it, but how to prove it?
"Judy, your nickname growing up was Tiny. Your favorite color is green. You got in trouble for stealing those M&Ms when you were 6, " said John.
"How'd you know all that? Why would John tell you that?"
"Because I'm John. I know everything. Mom used to lick her lips when she was up to something. Cousin Tommy spent the summer before high school with us, and we build that thing in the garage. I swear, I'm John," said John, in the body of a hot blond in nothing but a bra and a lacy thong. Judy put her phone down.
"But how? why?"
"The how is that medallion that is somewhere around here. The why is that I was planning on turning into Brad, but his jersey was last worn by Amy. I figured, if it worked, I could change things about myself after 12 hours. If it didn't, I would get a good laugh. Now I'm totally like this."
Judy sat down on the couch next to her brother and brought her hand to his face, tracing his button nose and plump lips, "Amazing..."
"What's even more interesting, is that this body has some preferences I didn't. Like, I had wine instead of beer"
"You are also talking differently."
"For real? I guess you are right," said John, "Anyway, I should probably find the thing and make sure it is safely stored."
"Can I try something? I have some clothing from a couple years ago I'd like to use. I'd like to be a little younger."
"Sure thing Tiny. I'll be here looking for it, see you soon."
"You are calling me Tiny? You're 3 inches shorter than I am now. Could you do something else too?"
"What do you want, sis?"
"Could you put on some pants?" asked Judy. John looked down, seeing his bare legs over the breasts on his chest. He nodded and went to find his pants and then the medallion when Judy left the condo. 40 minutes later, Judy was back and found John in the yoga pants and the football jersey watching some cartoons. Judy held up her dress she wore from her daughter's high school confirmation a few years ago.
"You don't want to be 25 again?" asked John.
"Not right now. I just want to be a bit younger, something I can be long term. I'd be getting a few years of my life back to enjoy with family and friends. My knee won't have that clicking I have from tripping at that party last year. Maybe I can become my 25 year self later when I have a free day. Here, pass over the medallion."