This part is interesting too.
"They found that children born to women who are 22 to 24 years old have a 29 percent higher risk of schizophrenia than those with mothers in their early 30s. For children born to mothers 15 to 21 years old, the risk of schizophrenia jumps by 76 percent."
https://www.spectrumnews.org/news/parental-age-different-impact-autism-schizophrenia/
I wonder why younger mothers have a higher chance of giving birth to a baby with schizophrenia.
The first thing that popped into my head when I read this was that I think the current belief is that schizophrenia can be brought on by a multitude of factors, including social and economic factors, and the younger the parent, the greater the chance that the environment is less stable.
A quick Google search indicated that higher rates of schizophrenia are also associated higher rates of poverty and social deprivation.
I would suspect, though I could be wrong, that it most likely isn't due to biological age in and of itself -- rather, it's more about the psychological, emotional, and financial state of the parents rather than just the age. The biological age of the parents COULD have something to do with it, but I think it's important to consider the extra challenges most young parents face.
In today's society, young people ages 22-24 may not be in as stable of relationships/marriages, job positions, living conditions, or financial stability as people in their 30's, therefore unable to provide a stable home environment.
And how much more severe are the conditions for those who are only 15-21? At that age, it's even less likely that the babies will be born into financially or emotionally stable conditions. Maybe they are being bounced around from household to household with different rules and personalities, maybe they are deprived of basic necessities (like proper nutrition or even enough food at all,) and the supposed adults who are raising them don't know how to live independently themselves, let alone raise babies.
Now I'm certainly not saying that anyone facing these hardships will develop schizophrenia -- we know for a fact that this isn't true. I'm also not saying that people raised with everything they need will never develop schizophrenia either.
But what I am saying is that I think it's a mistake to focus in on the age of the parent as a possibly higher risk without also looking at the wide variety of other factors that can't be denied when assessing human development.
It's not an absolute of course, but older parents are just more likely to be able to provide for their children, both financially and emotionally, because they have more experience and may have better-paying jobs, which might make it more likely that they will raise better-adjusted children.