Ruto decides to use magic to have them meet in the middle, at eighteen or so.

Of course! With her sage powers, she knew a way to even out their ages! Despite now being a young Hylian boy, Ruto was still the Sage of Water, and used her powers to teleport to Lake Hylia. Once there, made her way to Kakariko Village. It didn't take long to find Link, who was in the graveyard, looking around. She turned to see Ruto, and laughed. "Hello, little boy? You look a little familiar, have we met?"

Gathering up her magic, Ruto decided to play the young boy card. "No, miss, I don't think so! I'm new in town. Nice to meet you!" Link extended his hand for a handshake, but the second Link's hand touched hers, the spell activated. Ruto watched in fascination as Link grew younger, her height dropping and her confidence faltering. At the same time, Ruto's own body was changing, growing taller, more muscular, and more handsome. When it ended, Link was a teenager, barely an adult, though her Gerudo outfit still showed off a beautiful pair of breasts and her pants were clearly tight around her large butt. Ruto's mind seemed to focus on that, on Link's sexy body, and she felt a strange sensation in her pants that she'd never felt before.

"Hello? What did you just do, kid?" Link asked, snapping her fingers in front of Ruto's face.

Snapping out of it, Ruto smiled at Link, then laughed. "Hohoho! You thought you were rid of me by turning into a woman, eh Link? Well the tables are turned!"

It was clear from her face that Link was confused, but then she put two and two together. "Ruto!"

Ruto smirked at her, enjoying her surprise. It was also nice the way she saw Link's eyes move over her older body, the feeling of being checked out by her turning Ruto on. "That's right. Now then, are we going to fulfill our marriage promise, or not?"