I was looking through an old suitcase full of documents I got that belonged to my grandfather, and I found a postcard his mother (my great-grandmother) sent to her oldest daughter (his older sister) in 1923!! 
99 years old!
What is the oldest postcard you have in your collection?
I have a collection of old cactus and palm tree postcards. The oldest dates to 1906. And a number are from 1907. 1900-1915 was the “Golden Age of Postcard Publishing.”
My oldest card is from 1907.
I bought this postcard on eBay - it was mailed in 1938 and I don’t know either the sender or the received, but I have a small story about the card.
The card shows the Italian destroyer ship “Folgore” in the Venice lagoon. My uncle was a radio operator on this ship, which was sunk during a naval battle a few years later, in 1942. His body rests at the bottom of the sea.
I’ve never known him: all I have are a couple of photos and a medal our family was given after the war (because all a family is left with when a young beloved man is gone is a medal of military valour - how stupid is war?).
But still, I like to imagine he’s in this photo, somewhere on the ship, and I feel a little closer to him. 
I have lots of postcards from the first half of 20th century. Also from the beginning. Can’t remember if there has been one or two from before 1900 (is it possible?). But to be honest I just keep them because I don’t know where to sell them on a trustworthy/fair basis.
My father-in-law bought an abandoned farmhouse in Kansas, and we found a lot of antique postcards there. This one was sent to NYC in 1924 from Mexico! 98 years old.
I have a bunch between 1900-1910. I bought a large lot of vintage postcards in an online auction that I resell on Ebay…
These wonderful heirlooms, the oldest is 1909!
I don’t think this is my oldest postcard, if I recall correctly I have one that’s postmarked 1906 at my mom’s house. But I bought this at a local antique shop for about 72¢ yesterday.
It reads “Dearest Mama I give you this in remembrance of your 34th birthday. from your ever loving dutiful daughter Gladys September 15th 1913”
My love of history and postcards is well known to family and friends… so I’ve been gifted many old cards that people don’t want to throw away but don’t know what to do with. I also inherited a collection from my grandparents and great grandparents that is very dear to me. Here are three of my oldest.
The first I believe is from 1886, although the postmark isn’t clear, and it discusses groceries of all things! The second is a Happy New Year card from 1902 (you can see it was nibbled on at some point).
The final card is one of the oldest I have with a personal connection, from 1935. It was sent to my great grandfather (although I haven’t figured out his connection to the sender… yet).
I have some from 1903.
I have two or three cards from 1898 and 1899. Bought at antique auction. I love antique stores and auctions, there’s always so much cool stuff. Old cards are a bit magical, I think.
