He doesn't. It's just a physical feature resulting from the Tailed Beast inside of him, like Naruto's “whiskers” on his cheeks.
It is stated that Gaara has his dark circles around his eyes because Shukaku won't let him sleep because Gaara will lose control if he does. After the extraction of Shukaku, Gaara still has these circles around his eyes.
A few years after the Fourth Shinobi World War, Hinata joined the Uzumaki clan after marrying Naruto.
Firstly, there's a lack of any real need to fly over the South Pole. There's a lot less airline traffic in the far reaches of the southern hemisphere than the northern hemisphere. For example, the southern hemisphere doesn't have the equivalent of those typically busy sub polar routes between North America and Asia.
No. It is not legal. It is prohibited under the Arms Act to possess one without licence. One needs to have a licence for any weapon even bladed ones if it is larger than a permitted size.
While it's not illegal, lying about your age does violate the Terms of Service agreement users must agree to when they sign up. And when parents help kids lie online, they're setting a poor example about good digital behavior.