I figured from the way you phrased it that you were probably 17, but if not I someone would have asked.
If you have met the requirements you should be able to get ukara on your birthday - the requirements to have it: to buy a gun, is to be an adult - but nowhere does it say you can't qualify for it sooner.
Airsoft guns are generally comparable by their internal and external quality.
The parts that matter, the barrel/hop assembly and the gearbox+motor are generally of similar design specification in all guns and more importantly can be replaced, while in many cases a more expensive gun will have better internals, the price you will pay will in a large part be for externals you don't 'need' - not unlike cars. I'm not saying buy cheap and upgrade, just buy informed, don't throw £400 at a gun and be surprised that someone else has equal performance from a gun (albeit not necessarily a stock one) half the value.
That said, some manufacturers of unmodified stock (out of the box) guns are of a quality significantly above others.
You can get a perfectly adequate setup for £130-£180.