Yea, 11 months would be about right on their ages.
I think they are still a little small to be showing breeding behavior yet, but I could be wrong. A few questions:
Did your girlfriend actually see it calling? Sometimes the light fixture can buzz and it can sound a lot like the frogs calling. Calling probably won't be very loud from outside the vivarium.
Where were the supposed courting pair? If they were under that log like they were when I saw them the other day, it might have just been a same place same time type of deal. Often times a male will call from an open place near the laying site.
It is very possible though, they are getting close to old enough. They were in a group of 5 at my place and sometimes if you get them into a larger viv (like yours) it could stimulate breeding.
Maybe we can figure it out next time I drop by your place.
Azureus, Tarapoto, Iquitos