nice, I used to have the i-drive 5.
There may be GT catalogues in the archives on here, have a look through those to see if you can find what year the i-drive 4 was produced in that colourscheme.
From memory my i-drive 5 was from the late 90's/ early 2000's, looking at the kit on yours it could be around that time period. Might be worth checking the model numbers on the front or rear mech if they are Shimano, as that will help you pin down which year it was produced in.
Any plans for it?