Typically you won't get any informations regarding release dates from oracle, so nobody knows for sure. You can look at the previous release dates and might be able to derive something from them but this is pure speculation.
As for now we don't even know what features *might* be included in forms 12, so I am curious why you want to know? It's not been so long since Forms 11gR2 has been released.
There is no formal date set but it is likely to be in 2014.