Some gliding clubs allow youngsters to start to learn to fly. The major disadvantage of starting too soon is that they progress quickly and become bored since they can't fly solo until they are 16.
IMHO, and my daughter's HO, gliding is much more interesting and exciting than powered flying; it is much like building your own roller-coaster in the sky, e.g. 0-40kt in 3s, then climbing with you feet higher than your head, then aerobatics or flying with birds of prey or in thermals with other gliders.
If interested, find a convenient club at
British Gliding Association >> Find a Club >> UK Map and ask them what is possible.