Mind in Pieces, I surmise from your posts that you're in Britain because of all your A-level talk! Maybe some of the US posts won't be relevant to you, because you're talking about what in America they call high school??

I don't think 19 is very old to be in (British) college. I used to tutor in one and there were lots of A-level students who were 19 for various reasons.

If it worries you, though (and uni is possibly in your future), you could look into doing a foundation course instead of A-levels? Lots of people do those well into their sixties, and you'll leave qualified to go to uni. You would have to check if the uni/course you want will take a foundation degree, though. ETA: Sorry, before I wrote that I totally missed you talking about it on the ephemeral second page!

It sounds like you've picked a good spread of A-levels that you're really interested in. That sounds like motivation enough to at least find out, eh??