It may take it longer to evolve they dont evolve right when the turn 4 yrs old especially if youve paused it. If you paused it at all during its life it may take it longer to evolve.
You know, if 5 or 6 is the average adult evolution age, then mine must evolve early b/c mine usually evolve at 3. But that might just be because I have never paused my Tamagotchi ever. But for some reason it takes all of my friends' tamagotchis longer than mine, even if they don't pause theirs. Maybe I'm just lucky???