The prompt is from the recent fan theory that Webby is older than the boys in the 2017 continuity.

Given that the writers said that she's a year younger than Lena…

Teenagers

"Happy birthday to you! Happy birthday to you! Happy birthday, dear Webbigail, happy birthday to you!"

"Aw, how sweet of you guys!" Webby beamed as her granny placed the cake on the table in front of her.

Huey immediately started counting the candles.

"Wait a minute," he interrupted, "I spot 13 candles on your cake. Are you really 13? You're pretty short for a teenager."

"You must be pretty tall for an 11-year-old," Webby shrugged, then proceeded to blow out the candles. Beside her, Lena chimed in.

"It's common for boys to start having a growth spurt at 10," the shadow-made-real teen interjected, "I'm not that tall either. You'll probably reach my height in 2 or 3 years."

"Aren't you a living shadow? That would kind of indicate that your body's not exactly what we would call normal," Louie spoke up, before Dewey elbowed him.

"How tactless," the middle triplet commented.

"My granddaughter also hatched prematurely, so that would be another factor in her shorter-than-average height," stated Mrs Beakley.

"She'll catch up soon enough though. I know I did," added Launchpad.

Donald handed Webby the knife to slice the cake.

"Hear you go dear," the triplets' uncle said to her.

Webby sliced the cake swiftly and with perfect accuracy.

"As soon as you catch up to the boys in height, however, they'll soon outgrow you again," Donald notified the birthday girl, "Because she was the older twin, Della was always an inch taller than me in height, but as soon as the teenage years came, I towered over her by half a head."

"I see. No big," Webby smiled as she replied perkily.

Once everyone had had several servings of raspberry birthday cake, the kids went off to play outside while the adults tidied up the dining room. Twilight had just arrived as the setting sun disappeared underneath the horizon several moments ago.

While Huey and Louie argued about which games to play – Louie was pretty sure that no one wanted to play a trivia game on a hot summer's evening, while Huey was adamant that they did – Webby, Lena and Dewey sprawled themselves comfortably underneath a tree.

For a while, everything was perfect – Huey and Louie's bickering in the background aside – and the atmosphere was peaceful. No dangers, no ghosts, no demons, and no witches. For now, time belonged to them, and the three ducklings savoured the placid aura in companionable silence.

Eventually, Lena spoke up.

"You'll be in college soon," she said to the younger girl.

Beside her, Webby looked up to her best friend in slight confusion.

"Pardon me?"

"You'll be off doing what normal teenagers do," Lena went on wistfully, "Going to high school, getting into sleepovers, achieving A-plus exam grades and the like. You have a new road ahead to travel."

Webby picked up on her friend's melancholy.

"And you'll be right there at my side," the birthday girl replied.

"How?" questioned Lena, "I'm just a shadow. Shadows aren't meant to play. They aren't meant to study. They aren't meant to hang out, or to go to school. One time your grandmother said, even though it was before you all rescued me, that I didn't have a bright future, unlike you guys. She wasn't wrong."

"Well, she was definitely wrong about sheltering Webby for almost all of her life," Dewey piped in, "And by the way, Webby doesn't go to school either. Beakley home-schools her. In fact, she also home-schools me and my brothers."

"And who's to say that you can't join us?" Webby finished.

At this, Lena sat up and pulled them both into a hug.

"You two really are my best friends," she breathed softly, tearful but overjoyed.

"Touché," responded Dewey, as Webby tightened her embrace on the both of them.