hello
the only thing you really need is customer service experience. Anything else is a bonus (ie second language, hospitality experience, )
So when you leave school I would advise you to get a job in a shop, restaurant, bar, care home, bank, telesales.... anything really. If you want to go to college/uni then try to work part time if possible because almost every airline needs you to have 2 years customer service experience. You could start now with a Saturday job at tesco/ a local charity shop / volunteering with elderly or disabled people.
And start thinking about which airline you want to work for so you can research research research and be totally prepared when you go to the OD.
xxxx