No.
Yes. An air rifle is not considered a firearm, thus a felons possession is not limited.
Yes, an air rifle is not considered a firearm by Texas or federal laws.
You will have to contact the California Department of Justice for a current, legal and correct answer.
When you say Air Rifle you are referring to a pellet rifle not a firearm. At present there are no 300 Cal air rifle being made.
Only if the scope is designed for air rifles. Regular firearm scopes are made different than air rifle scopes and many will break if used on an air rifle because the recoil is different than a firearm.
No. Not yet.
No
If it is BB or a pellet gun, yes. A real firearm, no.
The minimum age is 17 for an air-gun (rifle or pistol).
If it fires a projectile, it is classified as a firearm and you will need a licence for it. Your local District Firearms Officer will be able to advise you in more detail.
The power of most firearms is measured in the feet per second (FPS) that the projectile is travelling after leaving the muzzle. This is the same situation with air rifles, and can be measured by the use of a chronometer, which can be purchased at most stores that specialize in air rifles. Air rifle speeds can measure from 300-1000+. However, when the FPS exceeds 500 feet per second, the air rifle is considered a firearm (in most countries).