It's the lower end but 13 could still be YA, to be fair. @amandaallenphd.bsky.social is the expert on YA, but I believe it would also depend on the tone and subject matter as well, as to whether it was children's or YA.

This might also be a UK/US difference as high school starts at age 11 in the UK, there's no equivalent of middle school (so 14 is not a particularly pivotal age here).

I was assuming the A in YA meant adult, so at least over 16, and generally over 18. 🤯