Most UK airlines ask for minimum requirements i.e. Good general secondary education (which could mean anything), flueancy in English and a second language preferred, previous experiance of dealing with the public and first aid/nursing or similar experiance useful.
Each airline goes with thier own guidelines and in my experiance bend them if the person is right for the individual airline. More so than in the past airlines are taking on older candidate's purely as they have more life experiances.
One thing to remember at an interview they are going to test your English and Arithmatic, possibly your language skills, but more importantly how you interact with your fellow candidates and interviewers.
So while you may have all the requirements they are asking for you may still not fit in.
Having said all that. Your best bet is to apply to all the airlines, pick you most liked and go from there. However remember that thousands of people want to be cabin crew and at shortlisting time the neat application form and met requirements go a long way to getting you as far as the interview, the rest is up to you.
Good luck