Your Tama is normally a teen for approx 72hrs - if you haven't paused it.
If it has been paused, your Tama will be a teen for longer.
It's probably best to estimate when it will evolve into an adult based on the number of hours rather than the age in years because some babies start life aged 1 and some babies start life aged 0.
I seem to remember it depends whether they have been made with IR connection or Matchmaker or Re-set from egg...
Be patient - your teen will evolve soon!
Best, etc.
TamaMum