Two screenshots attached, from the First and Second editions of the six-inch Ordnance Survey map. You can see that the footrpint of the house is similar in both.
The First Edition was surveyed in 1865.
So it would appear that the house was built before 1865.
However it's not as simple as it would appear.
The valuation rolls for Inverchaolin do not list Glenstriven until 1895, when the proprietor was Walter Berry. Before this, he is listed as proprietor of Inveravigan (which is almost certainly the Invervegain of the maps) and of Woodlands in 1875 and 1885. He is not listed in 1865.
Inveravigan/Invervegain isn't listed in 1865, but a Col Duncan Campbell (not Cameron) is listed as a proprietor of Woodlands, and Patrick James is also listed as a proprietor of Woodlands.
You would need to get access to the Abridgments of Sasines to find out exactly what property was sold when and by whom to whom. These are not available online so you would need to get someone who is going to the National Records of Scotland or a library that holds copies of the Abridgments to search them for you.
But it looks to me as if Glenstriven House must have been built before Kennedy sold it to Berry.
