More and more companies these days are taking adult trainees, giving them a very short course, such as night school and then shoving them on the hangar floor which is where you really learn the trade.
They usually ask for some sort of engineering background, it is possible to go to college and sit your exams without ever having worked in the real world but these licences cannot be used until a level of hands on experience has been achieved.
Either way it is more about getting a break and a foot in the door somewhere, the wages are also not great whilst training but an unlicensed mechanic can earn anything between £15-35K a year and a licensed and approved tech can earn between £30-50K a year.
Hope this helps