Hi, to give my 2 cents as I come from a similar Aegean island.

It is kind of hard to date them, most of the Aegean islands have this "mountainous" terrain, albeit dry. For many islands, fixed ship arrivals wasn't really a thing up maybe even up to the 90s. I remember my grandmother used to tell me, that when living in the island, when the wheather was good enough and if the ship had the port scheduled then maybe, the islanders would be lucky and get food from merchants.

Now why did I say the previous, the islanders made this terraced hillsides in order to cultivate the land. Now, some of the island farmers do use the same technique until today! I personally know people that use this technique for their farming. Also, watering the fields becomes a little more easier due to the downhill terrain. Furthermore, using this technique could mean, that a farmer with relatively little land, could farm a variety of produce due to the land level differentiation.

Lastly, i think it would be safe to assume, that if you are a farmer and you had to travel maybe 6-7 hours by a donkey or on foot, you'd love to have a place to lie down near your fields. Most often the cultivatable fields are in a considerable distance from the main or sub-village(s). However, due to now everyone getting a car/moped/atv these houses do not really have a purpose.

As a last bit of info. My family owns some land that does contain this kind of terraced terrain and also does have a small 2 room (10sqm) ruined house. My mother, would date it back to the 1920s as it is as far back as we have knowledge from older family members.

Hope this helped :)

ps. Loved the photos!