Novelty Knife

How old does one have to be to sell novelty weapons?

I live in Washington state and understand that there is an age requirement of 18 to buy/sell blades,such as hunting and fishing knives. Would this same requirement apply for novelty weapons such as swords, battle axes, maces, etc?

I would strongly assume that it does.

Arnold Schwarzenegger wields a knife while talking about budget cuts in twitter video