It goes on to state:
Two studies conducted within populations of twins have reported U-shaped relationships with paternal age and ASD or social-emotional development measured by the Strengths and Difficulties Questionnaire [Janecka, Haworth, et al., 2017; Lundstrom et
https://pmc.ncbi.nlm.nih.gov/articles/PMC7396152/#:~:text=A%20recent%20meta%2Danalysis%20examining,may%20relate%20to%20these%20mechanisms.
But the increase in ASD risk among very young fathers is not nearly as high as with old fathers, and it's the over 40 population of the "U" that is increasing in number and has the much more significant risk.
Here is conclusion of another, more recent article, from the ABA:
A notable finding is that the risk of autism in children rises steadily with paternal age. For example, men in their 30s are 1.6 times more likely to have a child with autism than men under 30. This risk increases further with age—fathers in their 40s have a sixfold increase, and those over 55 are four times more likely.
https://doublecareaba.com/post/do-older-fathers-cause-autism#:~:text=Studies%20across%20multiple%20species%2C%20including,neurodevelopmental%20disorders%20such%20as%20autism.
And here's an article in JAMA:
There was a significant monotonic association between advancing paternal age and risk of ASD. Offspring of men 40 years or older were 5.75 times (95% confidence interval, 2.65-12.46; P < .001) more likely to have ASD compared with offspring of men younger than 30 years, after controlling for year of birth, socioeconomic status, and maternal age. Advancing maternal age showed no association with ASD after adjusting for paternal age. Sensitivity analyses indicated that these findings were not the result of bias due to missing data on maternal age.
https://jamanetwork.com/journals/jamapsychiatry/fullarticle/668208#
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