I personally have travelled as a YPTU since 13 and haven’t been asked for anything more than the standard documents. No consent letters nothing special was needed at CBSA and other border control agencies around the world. I assume he would be safe, but you never know

Only special procedure I had to do was to complete CBSA declaration on paper and see a officer at the booth as the kiosks do not work for people under 16 unaccompanied. Still, nothing but the standard where have you been how long you’ve been away how much did you buy etc questions.