It depends on the country that you live in. In the USA their is no age limit to use an Airgun. However in most states you must be 18 to purchase one.
in the UK you have to be with an adult until your 14
Yes.
to many deaths from the use of them
That depends on your parents and local law enforcement.
Yes it does and it will eventually destroy the seals. Never use and oil on an airgun always use Crosman Pellgun or RWS oil they are designed for airgun seals.
No: usually you must be over 18.
It's up to your parent's, but you must be 18 to purchase one.
To replace the spring on a HW57 airgun, first ensure the gun is unloaded and safely de-cocked. Disassemble the airgun by removing the stock, then carefully access the compression chamber. Remove the old spring and clean the inside of the chamber before installing the new spring, ensuring it is properly seated. Finally, reassemble the airgun, ensuring all parts are securely fastened.
Only if the airgun has a scope rail designed into the gun. You will also need an airgun scope not a firearms scope.
You can't it's not designed to be a repeater.
The highest velocity of an airgun is that of Evanix AR6 pistol which is 1000 fps.
If you mean to purchase Airgun's and airgun accessories, I think Airgun depot has great prices and fast shipping. Pyramid Air is very good as well I hear.
depends on where rats are. If in your house i recommend old school spring traps. if in shed i recommend getting airgun