I define backlog as "games not played (seriously) yet, but intend to do so some time".

In this regard my oldest GOG game would be Beyond Good and Evil, bought Sept. 2010. I wanted to play it, but I had massive problems getting it run on my machine - and after it got fixed I just had too many other games I was busy with.

The very oldest game I've never really played but still want to some day would be Ultima 5, bought in 1991 for Amiga. Back in the day I just wasn't patient enough to get into this game (and my English skills probably weren't good enough).

I thought there may have been something in my Steam library that's older, but that doesn't seem to be the case especially considering that I only buy games there that I really want. For better or worse, I'm a bit less restrained when it comes to acquisitions on GOG.

That said, does Master of Magic count? Probably not because I've tried it often enough and keep bouncing off of it. Mainly I never invested enough time to really learn how to play it. So I guess that one doesn't really apply. But three purchases made about a month later do!

Bought on November 12, 2010: Realms of Arkania 1+2, Waxworks, and Panzer General 2. For Realms, I actually fondly remember playing one of them in the nineties, but now every time I try to start up the first I'm always wondering whether I've got enough patience for such a 'hardcore' RPG; possibly my most installed/uninstalled GOG game. ;) As for Waxworks, I've always been intrigued by the game premise and its gruesome scenes from old PC mag rags, but for whatever reason I just never bothered to actually get around to playing it. Lastly, Panzer General 2 I never done anything with except install and run it to see if it works properly. I just remember that I kept reading how great it was when the game was in its prime, but surprisingly I never mustered enough real interest to actually play the damn thing.

oldest backlog games was Mean Street / Martian Memorandum. This is due to the fact I already played Mean Street. So I haven't get around yet.

Single game that I bought and haven't played yet - at all - Gabriel Knight 2 - the beast within. apparently i want to play if after replaying GK1, but other games (and life) get in the way.

And currently I'm playing Ultima 6 for the I don't remember how many times.... :-)

but to be frank. i'm buying games for my retirement (in a way). since i do have a home license of window 7 (so if my pc died then just buy a new pc and install it) I can keep playing it. worse come to worse, i can still install windows 7 legally inside a vm on top of whatever window version then (10 or what not) and still play games inside it.

that is the cool part about non-drm games that doesn't rely on external server and what not.

Age of Wonders Shadow Magic, purchased November 26th, 2010.

It's weird, I tried Age of Wonders a year ago or so and was surprised how much enjoyed yet I didn't continue as strategy games rarely makes me compulsive to continue and I think I got distracted by some other game at the time.

I agree that a backlog is "games not played (seriously) yet, but intend to do so some time." I wouldn't count games that only came as part of a bundle.

Probably The Cat Lady. It's a pretty heavy game that I keep putting off, even though what little I tried made a big impact on me.

The most recent one that I cleared was Pharaoh. I could never really get into it, but after trying I found it to be a really compelling game.

It's noteworthy that my oldest game is relatively new. I've made a concerted effort over the past several years to wind down my backlog. I'm down to under five now.

Some people have absolutely enormous backlogs, but you can definitely clear them.

I have a similar problem with Netflix, where I've got this glut of options, and I can never decide what to watch.

Oldest GOG not finished: Fallout (October 2, 2008)
Oldest GOG never played: Fallout 2 (October 2, 2008)
Oldest game not finished: Caesar 3 (mid 1999)
Oldest game never played: it's hard to say because I can't always remember when I picked up some of these discs. Maybe Freedom Force or Homeworld

Dragonsphere (May 5, 2011), although I actually tried to play it (played like 3 screens before the game crashed or something). Otherwise, Divine Divinity (May 10, 2011).

Oldest GOG still not finished: Beyond Good and Evil
Oldest GOG never really started: a tie between Goblin's Quest 3 and Lionheart - Legacy of the Crusader (just played a bit of the demo and the beginning, with no intention to continue at that time)
Oldest GOG never even installed: Broken Sword - The Sleeping Dragon (still have to finish Shadow of the Templars)

From GOG: Freespace+Expansion purchased Sept 10, 2008

Not sure what my oldest unplayed retail purchase is, but it's probably Supreme Commander or Gothic Universe pack (I believe I bought both in 2007)

My first purchase was during a large sale in September 2013. In addition to the freebies, I bought, and have not yet played:
-Blackwell Bundle
-Primordia
-Amnesia - The Dark Descent

From that first purchase I have played:
-Waking Mars
-Torchlight
-Papers Please
-FTL (over and over and over again)

Fallout. Started to play twice but can't find the damn water chip >_<

Want spoilers or you prefer to find it yourself?
Also,my oldest game in the backlog is Zork 3.

I put it aside recently (before finding the chip as well) after shooting someone I shouldn't have, then somehow falling into a massacre of the entire settlement... :)

Gothic.

Yes, why not. I think I read some guides but still can't find it.
Thank you :)
Hehe, that's funny. I hope you could avoid the massacre :D