Think and plan long term (which you won't!).
Get the best grades you can for A level and apply for jobs. Preferably airline or airport related but it doesn't really matter for the first one. What do people do when they find sonething they've lost? They stop looking. The same goes for jobs. Most people get a job then stop looking. Don't do that. Make it your mission to apply for one job every week no matter what and accept anything that gives you at least 10% more. If you do that you'll be able to save up for flight training and you'll be a commercial pilot in your 20s. (Which is better than most of us managed!). Save half borrow half is the safest option. How long it takes depends more on your expenses than your income. If you drink a lot, buy a nice car and have kids then it'll never happen. If you live at home during your 'uni' years, work two jobs and live like a monk then it'll take 2 years and you'll by flight training by 20. That's not even including the money you could save in the next 2 years working at weekends. Make it happen.