mk6 would be a no go, the white lcd and cluster in general uses a different protocol to the MK5 as its moved over to the newer BAP protocol, so you would have to replace every computer in the car. There was a fairly detailed info on the cluster part numbers recently think it was stickied in the technical how to, it breaks the part number down for year high line and speedo reading.
And the age issue is to do with chnages to the imobiliser code, to make it harder to clock a car, so you can fit the newer clusters to older cars but you need special equipment like the stuff shark have, as you need to communicate with germany to retrieve the code, rather than just copying the bin files from one cluster to another.
Will have a search for a link to the thread you need....
Sticky link to the info you need.
clicky