Ubuntu Studio comes out in 32 and 64-bit versions. Its release cycle is
every two years (I think, there is still some uncertainty about its
continued development) with only three year support compared to Ubuntu's
six month (every two years for LTS) release cycle and support for five
years (LTS) or 18 months (intermediate releases). Before 12.04 this project
was in trouble, but it may have worked that out because it was a successful
release.

I think that you will have to use a PPA to get the latest GIMP.