One can purchase water guns online from a number of retailers. They are available to purchase from retailers such as Amazon, eBay, Walmart and Toys R Us.
What state is the store located in? If your state has a firearms purchase limit, they will have to adhere to it. Besides that, does WalMart itself have a corporate policy that limits the number of firearms that can be sold to the same person within a certain timeframe?
In most states you must be 18 to purchase a BB gun.
In the U.S. no state that I know of limits the number of guns you can own, and there is no federal law restricting that. There are a couple of states that have a one gun per much purchase limitation, but in those states, you can purchase a gun every months for as long as you want.
No limit
Federal law to purchase from a dealer is 18 for long guns and 21 for handguns. For ownership or possession the federal age limits are 18 for a handgun and no limit for long guns.
The limit is how many you can afford.
There is no standard limit on the number of firearms. You can check the website for the airline you plan to fly. There is a limit of 11 lbs of ammunition in a checked bag.
'GunsAmerica' have a number of categories of guns available for sale. One can purchase rifles, pistols, revolvers, shotguns and tactical guns. One can also buy ammo from them.
Federal law is 18 for long guns and 21 for hand guns.
This varies greatly by locality. To properly answer this one would need to know what location you were specifically referring to.
There is no limit.