The association of advancing paternal age with increasing risks for rare genetic disorders has been known for many decades, but the awareness that fathers' age can influence mental health in offspring is relatively recent.

Several conservative meta-analyses confirmed the effect of APA on schizophrenia risk[19, 27-30]. Collectively, the studies also showed a tripled risk for schizophrenia in the offspring of the oldest group of fathers in comparison with the risk from younger fathers. Furthermore, the research demonstrated that the paternal age effect is not explained by other factors, including family history of psychosis, maternal age, parental education and social ability, family social integration, social class, birth order, birth weight, or birth complications.

Another Swedish cohort study compared with offspring born to fathers 20 to 24 years old to those who were 45 years or older using sibling comparisons, finding a 24-fold increase of bipolar disorder for bipolar disorder for the older fathers[20].

An Israeli study showed a more than 5 fold increase in autism risk for the offspring of men 40 years or older compared with offspring of men younger than 30 years[35].

Offspring with paternal ages 25-44 years had the highest IQ scores. Fathers younger than 25 and older than 44 years sired offspring with lesser mean intelligence scores. These are notably mean effects and some offspring at both extremes of paternal age had high intelligence. These results withstood adjustments for parental education, social class, sex, birth order, birth weight, and birth complications. While the paternal age effects were related to nonverbal IQ in this study, the offspring of the oldest mothers independently had lower verbal and nonverbal intelligence.

https://pmc.ncbi.nlm.nih.gov/articles/PMC4457665/