I went to several away games at the age of 14 and 15, either on my own or with mates of the same age.
Where do you think teenagers get their money? £17.50 is a fortune when you're doing a paper round, mowing lawns and washing cars. Even the rest of the older under 18s are at colleges or doing low paid apprenticeships.
Can you explain to me the logic of not making a youngster pay £17.50, but only making them pay £2 if they are with an adult who likely has a full time job?