Seeing the 10-year-old Eileen made Ty feel kind of gross, even if she was still very cute. But it gave him an idea. "Eileen?" he said quietly.
"Yeah?" she asked.
"I think we should both get back to a not-creepy age," he laughed.
"Definitely," Eileen agreed, giggling.
"But I have an idea for how I want to do it," Ty added.
"Go on," Eileen replied.
Ty shivered as he wished away a few years of his life. His body shrank and un-developed, his sexual feelings vanishing as he became a 10-year-old himself. As the two of them stood together naked, they felt super awkward, but giggled at their naughtiness, and dashed upstairs to wash up.
After showering and cleaning up all over, Ty asked quietly, "Have you guessed what I wanted to do yet?"
"To be honest, no," admitted Eileen.
"I figured it'd be fun if we developed together," the boy grinned. For a moment Eileen was confused, and then she felt a rush of pleasant hormones return to her body.
In moments, three years piled onto both of them, bringing them back to adolescence, and their eyes turned staring and lustful towards each other. Ty saw Eileen's curvaceous young figure restore itself, her chest budding into A-cup breasts, and Eileen's eyes dropped to between Ty's legs as his balls dropped and his shaft rapidly thickened and lengthened.
A further year came to them a moment later, and their bodies responded lustfully to each other's presence. Eileen watched Ty get hard, his shaft almost poking at her stomach, and Ty noticed Eileen's nipples perk up and noticed her rubbing her moistened thighs together.
They kissed as they felt their fifteenth year return to them. Ty was now back to his original age, of course, and Eileen realized she wanted to be the same age as him, at least for this. "Ty," she breathed against the kiss, "I want us to do this while we're both your age."
Much as Ty knew he should probably go older- he'd wanted to age both of them to 18- he couldn't turn Eileen down, and his body burned with fertile teen lust for her. "OK," he answered, the two of them shifting to lie on the floor. His shaft brushed along her slit and both of them whimpered. He positioned his cock so his head was settled against her pussy lips, and whispered, "I won't be able to stop."
"Good," Eileen replied lustfully, and felt him slip inside her, his pale hands clinging to her dark ones as he slowly filled her more and more, determined not to hurt her. Once his shaft had reached as deep as he could go, he pulled back and rapidly started pounding into her. Eileen's body shook with pleasure, her breasts bouncing pleasurably and her G spot being kissed by his head with each thrust, and she moaned loudly as she was fucked.
Ty panted lustily as he moved faster and faster, not letting his head slip out of Eileen's tight passage even for a moment. This was the best sensation he'd ever felt- combining the initial wonderous awareness of sexuality from the onset of puberty with the unfamiliar pleasure of the first time actually having sex was incomparable, far better than anything his hand or even Eileen's pussy earlier that day had made him feel.
Despite how good all this felt, as one might expect for horny teens having their first time neither of them lasted long. Eileen's whole body shook and she moaned inarticulately as Ty thrusting at her G-spot made her hit her peak, and when her pussy clenched around Ty's thick shaft, he felt himself shoot what felt like every drop of white seed in his balls inside her fertile depths.
As the two of them came down from the high, they both giggled and kissed messily, still coming down from the ecstasy of having fucked and bred like animals in heat and the thrill of their newly redeveloped bodies.