You don't need A-levels to do an ATPL. You do need them to get a job with most airlines - although the need for them is inversely proportional to your age and experience (ie the younger/less experienced you are, the more you need them).
However, more importantly than that, you do need to prepare for the possibility (even probability for the moment) that you may well not end up flying for a living. Non-A-level-qualified youngsters don't tend to get offered great jobs in any field. Think very carefully before you abandon these very useful qualifications. You're very young - you have plenty of time to qualify for whatever you want to do. Don't start stocking up the regrets cupboard just yet!