Hi and welcome to the forum.
The problem you uncounted with being unable to find information on Simpson Shepherd and Sons Ltd are that they were a very small cog, within small cogs, within wheels; this is the age old story of the distillery industry.
Simpson Shepherd and Sons Ltd, who as far as I know no longer exist, were whisky blenders based, as you say, in Aberdeen and as far as I can tell 'Fortification' was their only product. They were a subsidiary, along with others, of the London based group J&W Nicholson & Co Ltd. In 1982 the Nicholson group was acquired by Allied-Lyons plc. and the production of the Nicholson products was transferred to Stewart & Son of Dundee Ltd (a subsidiary of Allied-Lyons). Allied Lyons in turn merged with Pedro Domecq in 1994 to form Allied Domecq. An acquisition for Allied Domecq was made by Pernod Ricard SA. in 2005 and as a result some of their newly acquired spirit brands were sold off to Fortune Brands and Diageo, but I think by the time we get to this point in the history of the whisky industry Simpson Shepherd and Sons had been lost in the mists of time.
As to the age of the whisky, Fortification - Old Scotch Whisky was a no age statement (NAS) product, so consequently its age is determined by the age of the youngest whisky in the blend. Under Scottish law a spirit can only be defined as a whisky after it has been matured in oak casks for a minimum of three years, therefore we can assume that this whisky is three years plus and as we don't know the makeup of the blend it is not possible to say how old it is, remember whisky doesn't mature in the bottle so, for example, a bottle of whisky with an age statement of 10yo remains a 10yo no matter how long you keep it.