Lawrence wrote: Although the age is then dirived from the youngest cask in the group.
Which is one of the reasons that some bottlings containing a high proportion of very old sms - the original The Glenlivet Archive from the 1990s springs to mind - have no age statement. If an age statement had been added, it would have to have been that of the small amount of relatively young TG that was added to the vatting to get the strength up to 40 pc abv or more, thus giving the consumer the impression it was pretty run-of-the-mill stuff.
The old TG Archive No-Age was a pretty tasty dram, imo.