I am not sure that the Law in this country would or would not apply,as it is against the Law here to sell certain knives to persons under 18 years of age, and indeed to actually sell certain knives( it doesn't state the person has to live here) I personally would at least get some sort of ID to support the sale, if for instance the knife was confiscated by Customs either here or abroad, there could be a backlash.................some of the Laws regarding certain states are a bit confusing, for instance in most states there is no such thing as an illegal knife( not to be confused with a knife, as a weapon, for instance carrying a pocket knife with a blade over 4 inches, opened and concealed, as in a purse, would constitute in some states carrying a weapon) another instance would be carrying a Bowie Knife in Alabama would be an offence, yet carrying a flick knife would be OK,iin a lot of States its an offence to carry a concealed knife if you are under 18, .
One would need to know the Laws in each state if you are going from one state to another as this would invoke federal law, as well as state law, and even local law, its just as well the knife laws in the States are lenient, its nice to see that even when they have updated their laws most states have not gone down the "knee jerk" route our Government has.