One question: For how long was it on the teenage stage?
The time when it evolves depends how long has it been on the current stage. It takes 72 hours/3days a teen to evolve into an adult. The age display meter is sometimes behind the right age. Have you paused it much?
That has happened to mee too by the way. My batteries run out and my Tamagotchi lost a year. Plus Tamagotchis are usually still 3 when they evolve into adults (they become 4 later on the same day) so that explains it all.
U PROBABLY GOT A SECRET CHAREKTER I DONT KNOW THE NAME FOR IT. A SECRET CHAREKTER [ONLY ONE] SKIPS BEING A TEEN/ AND TURNS TO AN ADULT. ITS WEIRD I KNOW!