I need more details, how long has it been a kid? Have you paused it or changed it's times often? Do you reset and download it often? If you answer these I might be able to help.
If you have paused your tamagotchi in the past, then it will take longer to grow. Also if you have changed the time for some reason, it can mess up your tamagotchis growth, making it grow super fast or super slow.
Have you bought your Tamagotchi online? because there was a case with the member, 'Starbucks' in which their tamagotchi was not aging, they had bought theirs from ebay and it might've been a glitch. Please read it if you have the time. It's very interesting.