As for America:
Under the Constitution, all Americans over the age of 21 have a right to bear arms, which in turn also allows Airsoft guns.
Airsoft is also officially recognised as a sport there, in Australia it is not, yet, haha 
Under American Federal Law, airsoft guns are not classified as firearms and are legal for all ages. This is also the case for the laws in each state. However, in some major cities and population centers the definition of a firearm within their respected ordinances includes propulsion by spring or compressed air, thus making airsoft subject to applicable laws. For example, airsoft guns within the state of California can only be bought by a person above the age of 18. However, no laws indicate an age requirement to sell airsoft guns. The seller must only verify that the buyer is 18 or older.
T
oh! there this to
"Imitation firearm" does not include: (1) A nonfiring, collector replica of an antique firearm developed before 1898; (2) Traditional BB, paintball, or pellet-firing air guns that expel a projectile through the force of air pressure; or (3) A device: (A) For which an orange solid plug or marking is permanently affixed to the muzzle end of the barrel for a depth of not more than six millimeters (6 mm); (B) For which the entire exterior surface is predominately colored other than black, brown, blue, silver, or metallic; or (C) That is constructed of transparent or translucent materials that permit unmistakable observation of the complete contents of the device
Poll