As much as I understand your frustration for not being admitted to attend a Prodigy gig, I must say I don't think your age is the problem, I would say, "some" other attendees attitude is more likely to be the reason why they ask for audience to have a certain age.
I went to see them last year in Vigo-Spain, ...I am used to going to so many concerts, and watch them from the front rows, without a problem, ...so I didn't think anything of taking my 12 year old cousin...as there wasn't anything said as for minimum age there.
I soon regreted my decision, We were around the 3rd row, and it was really hot...with the opening act everything was just fine...but as soon as The Prodigy came on stage, that very same audience turned wild, ...I thought we were going to get stamped on the floor, and nobody would notice, ...in fact the ambulance had to intervene, to take some people from the front row...NOT NICE!...as it was so hot, you could hardly breath, and Keith kept encouraging the audience...***k You!!!

I normally find this hilarious, but suddenly this wasn't fun to me anymore. LOL!
Fortunately we managed to get out of the heat, after a huge struggle we squeezed our way to a few rows back...and then I was fine with it, and was able to enjoy a GREAT concert!! ,but I would have loved to have been in the front rows, as I was when the concert started.
The Prodigy rocks!
Hope this answers somehow your question...