unless you find an ojitchi for it to mate with, then it will die. Or if you have 2 tamas, then let one be a boy and pause your otokitchi until the other grows to ojitchi. (youll get the secret char. on those too.) mate them and theyll have babies!
But I thought the matchmaker stops coming if your an oldie?
As a matter of fact the only way to get an oldie is to always reject her, if you have a baby, your adult tama will leave before turning into an old tamagotchi.