To be fair, the photo of the rainbow jumpsuit drag artist isn't from the company that are running this camp in Oxford. It's a picture of the unrelated DQ Storytime. I presume the local news site has stuck that on as a stock image.
14-18 is maybe because this is advertised as related to theatre and performance, so may be hoping to appeal to gcse and a level drama/performance/theatre/art students.
Drag is adult entertainment, it should be 18 plus only. If any teen of mine asked to attend it would be a clear nope from me. With a full explanation why!