Yes, messing around with the clock and pausing it can cause that to happen. Of course, it can be a glitch. I had my teenager at the age of 1 too, and I had my adult at the age of 2. You are not alone
Also I would like to add if your tamagotchi does not age sooner you could possibly reset or download. Also sometimes your tamagotchi won't age at the same time.
that has happened to me too. It was not a glitch. I think some Tama have a different growth patten. I might be wrong but i really think i am right. Tell me if anything changes!!