Can’t add callings

I am trying to add a second 14 year old YW advisor and can only have one. Is there a limit on advisors? I have noticed this on other callings recently. If it’s due to a limit on people in that position is there a listing of all callings or the callings in the website are it?

I don't know of any list, but in this case, the answer is in Handbook 2: 10.3.4

The bishopric may call one Young Women adviser per class and additional specialists, as needed, to help the Young Women presidency with their responsibilities.