Ty realised that he and Eileen now both had powers since they shared the same body, but also realised that they could override one another's wishes if one of them wished for something the other was uncomfortable with. Understanding this put his mind at ease about her powers, and so he asked, "Do you wanna try using them, then?"
"Yeah," replied Eileen. "I was thinking, how about I wish that our body would develop, be born and age to 18? I kinda don't want to just sit in a womb for nine months."
"Good point," Ty agreed. "I like the idea of being older too. Go for it!"
Eileen made the wish, and they both felt their body rapidly develop. It turned in moments from a xygote to a foetus, formed all its limbs and organs, and its sex was assigned. "This is weird... whoa, I have a penis!" Eileen remarked in their minds as she noticed their body's genitalia had developed.
"Oh yeah, I didn't really notice," Ty laughed. "I guess because I had a Y chromosome, when I turned into a sperm I kept it and passed it on when we got conceived."
Soon the body of their mother gave birth to them, and as they saw their new form in the light it was Ty's turn to be surprised. "Wow, our skin tone looks so different!" he commented, their newborn form crying quietly under the level at which they both spoke.
"Yeah, it kinda looks like a mix of both our tones," Eileen said. "I guess that'd make sense given this body was made from both our genetics."
As their mother cradled them in her arms, Ty and Eileen's body shifted into a void apart from the rest of the world, and they saw it age into adulthood. It shot through childhood, growing up and passing into puberty, at which point their libido re-emerged physically and their genitalia grew. Ty could tell Eileen was shocked by the sensation of having an erection, though she seemed to like it in a way. At last their body hit 18, and the young man they had formed was back down alone in Eileen's bathroom.
Following a moment's hesitation, he stood up and looked at himself with satisfaction. "Wow, I look pretty handsome," he spoke, reflecting Eileen's perception.