I believe he should be fine since IRCC gave the AOR anyways and did not say otherwise, Please see this link, one can argue that its the date you submitted if it was a complete application. https://www.canada.ca/en/immigration-refugees-citizenship/corporate/publications-manuals/operational-bulletins-manuals/permanent-residence/non-economic-classes/dependent-children.htmlGot Aor in june, he was 22 at that time, that means he is not a dependent anymore. But when I submitted complete application he was 21 then.
'Date IRCC receives a complete application for permanent residence from the principal applicant (for parents and grandparents, this applies only to applications received on or after January 1, 2014)'