There isn't an admin panel this is totally bespoke forum software.
This was chosen to be added as it prevents users searching for old threads and bumping them when they are no longer relevant, a thread without posts for 3 months is seen as outdated and normally contains outdated information. In the case a thread does need unlocking a moderator can do this at their discretion, just PM them and they will help.
This policy has been used on the main TGC forums for more than 8 years now and works well to manage old threads bumping.
The exact amount of time that we wait before locking a thread may be altered depending on forum activity but at the moment 3 months seems to be filtering most of the outdated threads.
Windows 7 Pro, Intel i7 3.8 GHz (Passmark: 9021), 16GB DDR3, NVIDIA GTX 780 4GB Superclocked (Passmark: 8056)