Nope. It may, however, be against a particular store's policy to sell hot or pointy things to people under 16 / 18 / 21 / 25 (I have encountered all four age limits in recent months). If this is the case at your local store, I would politely ask to see the manager, inform them that they have no legal reason to refuse to sell you the soldering iron (beyond "the management reserves the right"), their decision may be illegal on grounds of age discrimination, and you are going to take your business elsewhere. I would also get your friends to go to the same store, ask to buy a soldering iron and then give the same little speech as above when refused. If the store agrees to sell them the iron, when they refused you, they should refuse to pay until the manager explains why and offers you an official apology.