Why do so many people believe that 21 is the minimum age to purchase a handgun?
Is it because they misapply the federal age restriction placed upon federal licensees in 18 USC § 922(b)(1) to everyone else?

(b) It shall be unlawful for any licensed importer, licensed
manufacturer, licensed dealer, or licensed collector to sell or
deliver -
(1) any firearm or ammunition to any individual who the
licensee knows or has reasonable cause to believe is less than
eighteen years of age, and, if the firearm, or ammunition is
other than a shotgun or rifle, or ammunition for a shotgun or
rifle, to any individual who the licensee knows or has reasonable
cause to believe is less than twenty-one years of age;

I understand that some non-licensees will be similarly restricted by their resident state law, but in most states the age is 18 which matches the minimum age defined by federal law for everyone else in 18 USC § 922(x):

(x)(1) It shall be unlawful for a person to sell, deliver, or
otherwise transfer to a person who the transferor knows or has
reasonable cause to believe is a juvenile -
(A) a handgun; or
(B) ammunition that is suitable for use only in a handgun.

…(5) For purposes of this subsection, the term "juvenile" means a
person who is less than 18 years of age.

(Ref: http://trac.syr.edu/laws/18/18USC00922.html for the full law)

So in most states, under 21 handgun purchases from non-licensee private sellers are not only legal but quite common. So why do you think so many people still claim it’s a federal crime?

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Saiga AK-47 7.62x39mm Rifle

Group A: People who go to licensed dealers and gun show and purchase their firearms where they are registered with the federal authorities. They obtain permits to carry concealed firearms after hours of safety training and hundreds of rounds of practice fire and after intense scrutiny into their criminal record. They spend hundreds and even thousands of dollars on high end firearms and ammunition that is held to the highest level of quality and safety control. They spend hundreds of hours and countless rounds of ammunition a year at the range. Some are former law enforcement and military personnel. They are some of the safest firearms operators on the planet. They purchase their weapons for hunting, sport, to exercise their God given right, and to assure the safety and well being of themselves, their loved ones, and their property. What they DO NOT do is perform drive-bys, knock off Seven-Elevens, mug people, and commit murder. For that matter they don’t commit hardly any type of crime because they have to maintain their permits to CCW.

Group B: People who commit murder, perform drive-bys, knock off Seven-Elevens, mug people, and generally have little to no regard for the law. What they DO NOT do is purchase their guns from licensed vendors or register them with law enforcement. They do not purchase high end equipment and ammunition from reputable dealers. They do not obtain legal permits to carry concealed weapons. They do not go through training in weapons use and safety. They do not go through any kind of screening process to weed out criminals (because that’s what they are). They purchase their fireams for any one of the aforementioned reasons

You still with me?

Now, using gun grabber logic, you can stop and prevent Group B from committing all the terrible things they do by taking guns away from Group A.

If you disagree, then please enlighten me.
Mountain Man,

To acquiring a CCW in Ohio requires an intense background check and a 17 hour training class that covers safe operation, accuracy practice, and the mental preparation to use a firearm in self defense. By the end of the course each participant will fire approximately 200 rounds of ammunition at the range. Please don’t tell me I’m wrong when I clearly have more knowledge on the subject than you.

http://www.moftaohio.com/classes/concealed-carry/

Eddieroachr

I think you would agree that a straw buy would fall under the canopy of "illegally purchased". Law abiding citizens tend to do just that; abide by the law.
Mountain Man,

Aside from the fact that I think you have a myriad of your own issues, I disagree with the idea that you can affect a group of UNLAWFUL people by making new LAWS. The only people that will be affected by NEW gun legislation are people that obey CURRENT gun legislation (i.e. Group A and not Group B).

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In the early part of the last century, the nation tried to ban alcohol. The result was speakeasy’s, rum runners, bad liquor, and organized crime.

In this new century, an Obama Administration along with the Democrats in Congress might try to "effectively" ban firearms ownership through heavy regulation, ammunition taxes, and mandatory federal licensing of gun owners.

If this comes to pass, could there be a new Prohibition Era based upon guns instead of liquor? "Gun" Runners instead of "Rum" Runners?
To FireBug below,

The Fed’s don’t outright ban guns, but the enact so much petty and hindering legislation to make it a P.I.T.A. to own a gun that some folks just give up.

Example: If they pass a 100% ammunition tax, that’d drive away a lot of the casual shooters; it’d just become too expensive.

Same with federal licensing. Many folks might refuse to obtain a federal license or pay some outrageous fee for one, and therefore just give up on being gun owners.

It is the strategy of incremental legislation the anti-gun crowd uses to slowly, and eventually completely, erode our gun rights.

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Here in Canada, we have large sporting goods stores, and we have numerous gunstores where people can purchase hunting arms such as shotguns and rifles, along with ammunition. Handguns can also be purchased with a license; it is not that difficult to obtain if you do not have a criminal record.

When I go deer, turkey, duck, or elk hunting, I usually have most of my gear already in storage at my house, and if I need to replace something (such as a torn pair of camouflage pants, or a hunting knife), I just drive over to the sporting goods store.

Stores like Canadian Tire also have a good selection of hunting equipment.

Is it mostly the same in the UK? Where do you lot usually purchase your hunting gear? Hunting is very popular across Canada during this time of year, in the fall. Licenses are issued province by province, though.

So for instance if I wish to hunt turkeys in Ontario, I contact the Ontario Ministry of Natural Resources instead of the federal government. How does it work in the UK?

Be sure to read the comments, you will find more information about federal firearms license