No, If you are under 18, it is a criminal offence for anyone to send you material inviting you to borrow money or obtain goods or services on credit or hire purchase. However, if you are over 14 but under 18, you can enter into a credit or hire purchase agreement if an adult acts as your guarantor.

http://www.adviceguide.org.uk/index/your_world/consumer_affairs/young_people_money_and_consumer_rights.htm

Be aware though that a subscription to a annual membership can be very different to a consumer credit agreement, a credit agreement only exists if they have lent you some money and you are paying it back plus interest...this is not applicable where you pay the subs monthly or upfront for a year.!