There is a lot out there questioning the growth of a V2/V3.. From what I have noticed bad care parents decrease the odds (slightly) in getting a good care teen. Let's bring my current generation on my V3. She was mostly sleeping, and only awake for a few hours. She got some training. She started out as a tamatchi cool beans a different toddler for me. And during her toddler stage she was sleeping during the day and awake when I got home until I went to bed. So she got really good care, and instead of a good care teen I got Hashitamatchi a bad care teen. And from what I have seen in long term generation logs on these tamas, weight, turning the light off, how well you can keep the meters full, cleaning poop asap, and training and so on all influence which care level you are found in (perfect, good, average, below average, and rotten). But also I think the parents also influence it, ie with bad care parents its harder to get a good care teen and adult, with good care its easier to stay up in the good care and harder to fall all the way down to rotten
And again it also falls on random number generators and chance within each tire you have equal chances of each character