John was more than a little mystified about what happened. He got a call to do a babysitting job and what he got wasn't what he expected. First of all, these two scantily clad women were waiting for him there, obviously getting ready to go to the beach party downtown. Secondly, they wanted him to watch over a baby that didn't look like she could be connected to either of them. Third was their method of payment in which he could squeeze their boobs, which he had to admit was not a bad deal even if there was no money. Finally, there was that thing the bustier one said, about putting the baby in the Jacuzzi if she was 'too young for him'. John had no idea what that meant, but he was tempted to find out.
Going into the bathroom, he could see that Jacuzzi was already filled up and covered in blue foam. He carefully lowered the baby into the water. The water felt rather cold, so John pulled out the drain a bit before turning on the hot water. He kept his hand in the water to make sure it would be warm enough.
John didn't pay attention to when he felt the first tingle but when the second tingle hit him, he felt his shirt go up. He stood up and quickly noticed that not only was he taller, his clothes didn't quite fit as well as before. Looking in the mirror, he was surprised to see an older version of himself. Not too much older, having gone from 14 to 16, but those two years made a lot of difference. He was taller, his torso was starting to fill out with muscle, and his face was looking less boyish. He took off his shirt to take a better look at himself. He was definitely more muscular, his shoulders wider. But he wasn't quite the same level as muscles as the older boys he had seen. Nevertheless, it was enough to keep him fascinated with the mirror for quite some time.
But then John heard a girl's voice say, "You're pretty cute." He looked over at the tub and jumped a bit. Instead of a cute baby girl, there was a girl in her early teens with lovely golden hair. John could notice that her figure was starting to develop nicely and her breasts, though still pointy, showed signs of rounding out into something big. John quickly tried to look away only for the girl to giggle. "You don't need to be shy around little Kelly," she said before she gave a brief moan, her body growing a little larger, her breasts filling out more.
That name rang a bell for John. There was one Kelly he knew of. Heck, practically everyone knew of her. She was the wet dream material of pretty much every guy in town, including himself. And this blonde girl had an unmistakable resemblance to her. "Kelly Anderson?" asked John in surprise.
"The one and only," said Kelly, "Though a little younger than normal."
"But how is that possible?" asked John.
Kelly pursed her lips and said, "It must have been the shampoo. I remember using one bottle and getting younger. I nearly got too young but then someone rescued me."
"Then who were those women I talked to?" asked John before describing the two hot women that had left him in charge of baby Kelly.
"That sounds like my little sister Ally and her friend Jenna," said Kelly, "The other shampoo must make people older and that's what's in this tub."
"It makes sense," said John, looking at himself, "I had my arm in there for a while and I got older."
There was a slight splash and a moan before Kelly said, "How about getting a little older?" John looked back at Kelly and saw that she was now 16 years old. She wasn't completely curvy like the 21 year old self he knew, but she was definitely hot. And the look in her eyes was very inviting. "Just come in the tub with me. It's going to be an experience you won't forget," she purred.
Reason and doubt gave no protest as John eagerly started taking off his pants. He was a little surprised and delighted to see his penis had also grown, sticking out further than before. His balls also had some more hair than before. But what mattered right now was getting in that tub. It took a little maneuvering and some water overflowed with the added mass, but soon John was lying in the tub with Kelly laying on top of him. He could definitely feel their naked bodies rubbing against each other underwater as they made out.
The shampoo in the water continued to age the two of them in spurts. As Kelly got back more of her sexiness, John got more mature. His shoulders were widening farther as his chest expanded with muscles. His hands and feet were also growing bigger as the limbs they were attached to were getting longer and muscular. But of most importance to Kelly was the growth of John's rod which was pressing into her.
When they were both 18, Kelly made the next mood. She pulled herself away from John before climbing onto his lap. Expertly, she aimed her pussy at his rod and lowered herself onto it. John gave a lot moan as he felt her envelop him. It nearly knocked him for a loop when she started moving first, going up and down on him. John was quick to respond as he started thrusting. The two of them kept at it as they matured even further. John could hardly believe that he was really fucking Kelly Anderson. It especially turned him on as he watched her breasts bouncing and growing right in front of him. It was all the encouragement he need to thrust harder before finally hitting his limit and sending a burst of seed into Kelly. Kelly gave a cry of ecstasy as she also came.
John would have been content just to relax in the tub, but Kelley was getting out. "Hurry out of there if you don't want to get older," she said. That quickly reminded John that the water would keep aging him and quickly got out. Kelly was posing in the mirror, glad to be back to her sexy 21-year old self. The handsome man that John had become was certainly a bonus. "So, wanna head up to my room and continue?" she asked coyly.
"Already?" asked John, his voice deeper than before. He was certainly not opposed to the idea, but he didn't know that Kelly had such a large sexual appetite.
"Well, I do owe you a lot for making me my right age again," said Kelly, "Besides, you're just as good-looking as the other men I've dated."
"But what about your sister?" asked John.
Kelly frowned a bit before saying, "What about her?"
"She and Jenna headed off as adults, remember?"
"Oh, right," said Kelly, "Well, I'm sure they're smart enough to keep out of trouble. We can go look for them after we have some more sex."
"But-" started John but was quickly cut off when Kelly fondled his bigger shaft, "Whatever you say, babe."