Doesn't look like the legislation has passed through Parliament yet. I'll quote my blurb for those who aren't borderline. I know that the first and second paragraphs are conflicting - it's the difference between having permission and having the right. Where you see (*) is where the age change applies. The blurb I'm quoting is in italics.
The laws concerning the use of airguns by young persons are as follows:
Anyone under the age of 18(*) can only use an airgun whilst under the direct supervision and control of someone over 21, whilst on private property, with the permission of the owner of the premises or land, or at an approved shooting range or shooting gallery.
A person aged between 14 and 18(*) can use an airgun on private property where they have a right to be, without supervision
They may carry an unloaded and un-cocked rifle (but not an airpistol) in a public place only if it is in a securely fastened gun cover so that it cannot be fired. An under 14 year old must again be accompanied and supervised by a person over 21 years of age.
I'm not sure when the legislation change comes into effect so I'd check with your local police - just to make sure you keep on the right side of the law, if you've looked at articles section of the AETO site you'll know how severe the penalties can be.
A word of warning to those not considered old enough to shoot unsupervised - make sure your supervisind adult isn't banned from shooting as you'll be considered to be unsupervised and liable to prosecution, whether you knew or not.
Again I stress that anyone who is intending to go shooting (or even pick up an airgun) makes sure that they are familiar with the relavent laws.