Tamas sometimes show different ages to everyone elses.
The real age of the tama is based on how many hours it has been alive.
Baby = 1hour - then evolves into a Child/Toddler
Child/Toddler = 24hrs - then evolves into a Teen
Teen = 48hrs (V4) or 72hrs (V1-V3) - then evolves into an Adult
Adult = no time limit, but Matchmaker starts visits 72hrs after it evolves into the adult character
Some ppl's Babies turn 1yr when they are in the Child/Toddler stage - others Babies start their life showing 1yr old - so you see, the age really can vary from tama to tama (and even generation to generation). I think it might have something to do with what time of the day you name the baby and start the new generation.