In England, anybody over the age of 18 can buy an airgun, including PCP air guns. However, it has to be below the legal power limit of 12ft/lbs for an air rifle, or 6ft/lbs for an air pistol. You cannot have an air gun in public unless you have a reasonable excuse and you can only shoot where you have permission. 

If you’re between the ages of 14 and 17, you can borrow an air gun and ammunition and shoot it, without any supervision, on private premises as long as you have permission. However, you cannot buy, hire, or receive an air gun or any air gun ammunition as a gift, or carry it in a public place without being supervised by somebody over the age of 21 and with a reasonable excuse. 

If you’re under 14 years old, you can use an air gun if supervised by somebody over 21, on private premises, and with permission. You cannot buy, hire, or receive an air gun or any air gun ammunition as a gift and you must be supervised with the gun at all times.