Under the current terms each accompanying spouse or unmarried child under 21 adds a further processing fee and a further US$1 million gift. A 22-year-old falls outside that definition and cannot be added on those terms, so a separate route would be needed for that child.
Count the household, then find the person the terms exclude
Do the arithmetic person by person before forming any view about affordability. Hypothetical example: a sign manufacturer near Saint-Cyrille-de-Wendover plans for himself, his wife and two children aged nineteen and twenty-two; on the published terms the household comprises three people who fit the accompanying definition and one who does not, so the budget is a US$15,000 processing fee for each of the three plus his own US$1 million gift and a further US$1 million for each accompanying family member — and the twenty-two-year-old is outside it entirely.
That older child’s options are his own, on his own merits, and they should be explored in parallel rather than after the parents have committed. Note also the direction of a birthday: a nineteen-year-old who will turn twenty-one during a lengthy process needs the same forward planning, and the timing question should be raised with counsel rather than assumed away.