If something's inapplicable, it's irrelevant or unsuited. Laws that affect adults over the age of 18 are often inapplicable to children and young teenagers.
Even if something is true in one situation, it might not work or fit in another situation — it's inapplicable. A list of plants that grow easily in your aunt's garden in Hawaii will probably be inapplicable to your garden in New Hampshire. This adjective combines the "not" prefix in- and applicable, from the Latin applicare, "connect" or "join."