Sours can take 3 years in some cases. I have about 3 1/2 barrels in old Buffalo Trace barrels. It was acetone the first few month, then it soured, but not enough. To promote some more sourness, I took a handful of malt and just dumped it in there, soured right up. My thought is that is will eventually age out. Mine has been going for about a year and a half. With a little evaporation and filling the occasional keg, we end up with enough room to add fresh unfermented wort. In another year and a half, I'll blend it with fruit, package it and send it off to my distributor.
So, with that said, try aging it over oak chips and add a handful of grain, it might help.