Johnnie Walker

If you believe Wikipedia (as I do, of course) there is no "presumably" about it – altough the shop, even though it was in the county of Ayrshire, was in Kilmarnock, not Ayr itself. And you don't have to take Wikipedia's word alone; it cites the Cigar Aficionado, which tells the story in some detail. Its first paragraph reads:

"John Walker ... was born in 1805 on Todrigg's Farm near Kilmarnock in Ayrshire, in the Western Lowlands of Scotland. (Johnnie Walker whiskies are still bottled within sight of Walker's old dairy farm.) Walker was every inch a grocer, trading in anything and everything. Tea was his specialty; at a time when the British were planting China tea bushes in India, tea had had become a patriotic drink. He also sold raisins, vinegar and, of course, Scotch. By 1850, he was offering customers Walker's Kilmarnock Whisky, which soon attracted a small but loyal following. Its reputation grew as merchants and travelers on the new London to Glasgow railway line (which went through Kilmarnock) spread the word."

John Walker's son Alexander joined the business in 1856, and he persuaded his father to abandon the narrow realm of the grocery trade and to go into wholesale trading. Under John Walker (says Wikipedia), whisky sales represented eight percent of the firm's income; by the time Alexander was ready to pass on the company to his own sons, that figure had increased to over 90 percent.

Johnnie Walker whisky still uses the slogan "Born 1820 ... still going strong." This was the year in which John Walker bought an Italian warehouse, grocery, and wine and spirits shop on the High Street in Kilmarnock, with the proceeds from the sale of Toddrigg's Farm following the death of his father the previous year. Mathematically inclined readers will note that John Walker cannot have been more than 15 years old at that time. Wikipedia tells us that by 1825 he was selling spirits, including rum, brandy, gin, and whisky – even though he himself remained a teetotaller. It was in 1865 that Alexander created Johnnie Walker's first commercial blend, calling it Old Highland Whisky and registering it as such in 1867.

By 1906 there were three brands: Old Highland at 5 years old, Special Old Highland at 9 years old, and Extra Special Old Highland at 12 years old. These three brands (Wikipedia tells us) had "the standard Johnnie Walker labels": white, red, and black respectively.

It was in 1909 that John Walker's grandsons, George and Alexander II, rebranded the family's whisky lines and introduced the 'Striding Man' mascot which is still used today. The Old Highland labels were discarded, and the three blends have been known ever since by the colours of their labels. Johnnie Walker Red Label (the middle–range, 9–year–old brand – formerly Special Old Highland) currently claims to be "the best–selling Scotch Whisky around the globe."

John Walker died in 1857. So while it took him thirty years from setting up his family business (in the year of which the firm boasts in its famous slogan) to venture into production of his own brand, he did sell it for the last seven years of his life.