No, he must include them.
-The older child does not need to be 'included' as non-accompanying as no longer a dependent (IRCC uses > 21 years of age, i.e. at 22 no longer eligible anyway). He will include that child on the other family information form, he should include a letter that child not included because too old to be sponsored (because frankly sometimes IRCC gets it confused when children are older than the minimum age).
It will be FAR better if he can include the younger child as non-accompanying and have the child do medicals, biometrics. They will make the process longer and more difficult otherwise. This is not sponsoring, but reserves the right to do so in future. Even if he does not intend to sponsor the child, this is the better way. (And who knows, he may changes his mind if the kid wants to come study in Canada or somethign)