pretty sure all states have a 21 limit on handguns

Why do you want a gun? Dont do it.

State law restricts selling or giving handguns to juveniles under 21, and other firearms to juveniles under 18, except for supervised loans of firearms or for limited lawful activities (such as hunting). http://www.bradycampaign.org/legislation/state/viewstate.php?st=WA

Check in with your local Police or Local City Hall...

I live in Washington State. Even though federal law prohibits gun dealers from selling you a handgun until you are 21 there is no law prohibiting you from owning or possessing a handgun at the age of 18 and in Washington State it is perfectly legal to do so. There are some restrictions for those possessing handgun between the age of 18-21, but there are also broad exemptions that allow you to carry a handgun in certain circumstances at the age of 18. You will not be able to get a concealed weapons permit until you are 21. RCW 9.41.240 Possession of pistol by person from eighteen to twenty-one. Unless an exception under RCW 9.41.042, 9.41.050, or 9.41.060 applies, a person at least eighteen years of age, but less than twenty-one years of age, may possess a pistol only: (1) In the person's place of abode; (2) At the person's fixed place of business; or (3) On real property under his or her control. RCW 9.41.060 Exceptions to restrictions on carrying firearms: The provisions of RCW 9.41.240 shall not apply to: … [snipped for brevity. Only 6-9 could be applied in your situation] (6) Regularly enrolled members of clubs organized for the purpose of target shooting, when those members are at or are going to or from their places of target practice; (7) Regularly enrolled members of clubs organized for the purpose of modern and antique firearm collecting, when those members are at or are going to or from their collector's gun shows and exhibits; (8) Any person engaging in a lawful outdoor recreational activity such as hunting, fishing, camping, hiking, or horseback riding, only if, considering all of the attendant circumstances, including but not limited to whether the person has a valid hunting or fishing license, it is reasonable to conclude that the person is participating in lawful outdoor activities or is traveling to or from a legitimate outdoor recreation area; (9) Any person while carrying a pistol unloaded and in a closed opaque case or secure wrapper… Anti-gun lobby websites like the Brady Campaign are not a reliable source for information. You can find the REAL Washington State gun laws here: http://apps.leg.wa.gov/RCW/default.aspx?cite=9.41