As blenderm stated, for Scotch whisky, if there is an age statement, everything in the bottle must be at least the age of the statement - with exception (if used) of a coloring agent and water added to bring the whisky down to the bottling ABV.
So, the four malts listed on the back label, as well as others not listed, must be at least 15 years old, and whether they are malt or grain whiskies.
In theory, a 12 year Macallan could be a vatting of 13-20 year old whiskies. If so, they cannot label it as a 14 year old (or older) but they could label it as a 13 - or a 5 - if they wanted.
I agree with the four malts listed on the green label being today nothing more than shameless cross-promotion by the Diageo marketing machine. But, they are all good malts on their own, and Talisker and Caol Ila have long been staples in many of the Walker blends.
It'll be interesting to see if some of their classic components will continue to be as prominent a part of their blends once Roseisle has enough stocks at age?
The comment here is that Roseisle was designed to produce a range of styles of whiskies to be used in the Diageo's blends. If they want the iodine of some Islay malts in a blend, it can now be produced at Roseisle by simply ordering malt to a certain ppm of peat and distilling spirit to replicate what they want for their blend. I'm not saying they can make Islay whisky in Speyside; I am saying the uniqueness of each malt is lost in a blend so they're really only hoping to make something at Roseisle that gives them what they think Caol Ila allows them to achieve in their blends.
If I were a distiller who was selling to Diageo, I'd be very concerned right now that their ultimate plan is for themselves to produce their range of profile whiskies and cut the distilleries they don't own out of the blend. Thus, I'd be working very hard at developing my own brand, in the time those Roseisle stock are coming of age.
And for the distilleries Diageo owns, if a distillery is old and not as efficient as it need be for the mass production and market needs of the Diageo blends, I'm predicting a wave of distillery sales and/or closings once Roseisle has stocks to the necessary ages for their blends.
My point to all this, the malts listed on the green label may likely not be a part of the blend in the future? Of course, they may continue to be but much of everything else in it might be produced at Roseisle?
As Roseisle came on line in 2009, its spirit will start affecting red label next year, black label in 2021 and green label in 2024.
Finally, not all spirits with age statements have the same stringent requirements as the Scotch whisky industry. It depends on their local governing body. For example, a 21 year old rum might contain a thimble full of 21 year old rum, the rest being new make spirit and caramel color to make it look old. Even the VS, VSOP and XO labeling for Cognac has its limitations. I think understanding this ultimately guides people to Scotch - which leaves no doubt in my mind that the best distilled spirit in the world are made by the best malt distillers in Scotland.