The Strathisla Distillery in Keith Scotland has the oldest uninterrupted* distilling history in Scotland beating out the second placed distillery by 28 years.
I am unconvinced that a distillery which was established earlier then shut down for 40 years; then rebuilt on an new site may lay claim to such a title. Furthermore, if I then add up the total number of years this distillery has been operating from start to now, excluding the years it was not in operation, then it certainly does not add up anywhere near the oldest distillery in Scotland. The title as the oldest distillery in Scotland must go to Strathisla.
Glenturret was built in 1775. Strathisla distillery was built in 1786. Glenturret was built 11 years before Strathisla was built. No argument here. Glenturret closed down entirely early 1921, was dismantled; reopened June 1960 and produced filling malt before finally making a Glenturret single malt many years later.
Now lets take away the 40 years the distillery was shut down. The maths is easy and you will then discover that Glenturret continues distilling history is 199 years versus Strathisla which has an uninterrupted distilling history of 227 years.
*uninterrupted other than during times of war which effected all distilleries.