That's not what's happening all. The federal guidelines set a floor, not a mandatory number. It's like alcohol. You can't buy alcohol under age 21. But individual stores/bars can set their limit to 22, 35 or even 50. They just can't set it below 21. Similarly, a gun store can set their personal age limit to 21 if they choose, they just can't set it to 17 or less. And no, it's not an 18 yo's legal right to own a rifle. Some states have no minimum age for possession, just for sales. And you're equating the right to own a rifle with an obligation that someone sells it to them. No one is obligated to carry firearms for sale. Nor are they obligated to carry every variant of firearm accessory. If they choose to carry firearms or accessories, they are obligated to sell them in a manner that does not contradict federal and state law. And federal and state laws set minimum ages, not mandatory ages.