Not legal advice. There seems to be no Oregon law or administrative rule prohibiting the sale of lighters to minors. So while a store could always refuse to sell you one, there does not appear to be any legal bar to you buying one.
The state has however a clear mandate on novelty lighters:
Oregon law prohibits selling, offering for sale or distributing novelty lighters. It is also illegal to manufacture, import, or possess novelty lighters in inventory for the purpose of sale or distribution. Exceptions apply to lighters manufactured before January 1, 1980, and those that are permanently altered to prevent flame or other causes of combustion. Violations are subject to a civil penalty of up to $500 per day for retail sellers or distributors, $1,000 per day for wholesalers, and $10,000 per day for manufacturers or importers. The State Fire Marshal determines which lighters are novelty lighters and is authorized to inspect facilities, inventory, and records related to the manufacture, import, wholesale, storage, sale, or distribution of lighters.