I don't think so, I'm pretty sure age doesn't matter and you stand an equal chance to the rest of us, usually airlines actually prefer younger candidates. All you need is a love of aviation!
I say, if you would enjoy it then go for it!
If you would still like to do A levels, im sure you can work your way around it.
A levels, depend on the subject you take will run from May - June, only around 2 months after the course starts. I say you could give it your best shot and sit your a levels while continuing the course, make sure you use these next few months to really solidify and revise for your a levels so that you are confident by the time the course starts.
However, if this doesnt work, you could always sit your a levels in summer 2024, after the course has complete.
It is good to have A levels, as a backup, so i'd say you should still focus on your a levels, and see how everything goes! If you really want this I'm sure you can try manage both at the same time.
Best of luck.