I usually consider everything that’s cartridge based, plus the 1st gen, to be retro, though I might have to change that considering PS1, at least, feels pretty retro by now too.

Totally depends on your age. For me, the 16-bit era is retro, as I grew up with that generation. N64 and PS1 ushered in the modern era of 3D games, but it could be argued to be retro as well as it was still very early 3D.

PS2 era had online gaming and big productions with huge budgets. I would never call PS2 and GameCube retro consoles.

Not completely sure. Gen 5 definitely seems retro now, but I'm not sure about Gen 6.

If the console isn't for sale brand new anymore, it's retro in my eyes.

Meaning anything Pre-Xbox One/Playstation 4/Switch is Retro.

Maybe it's because I'm younger than a lot of people here, but I'm not really sure why the Xbox 360, Wii and PS3 wouldn't be considered retro. I got into gaming hardcore during the peak of the 360/PS3's popularity (and even earlier than that got into casual gaming with the Wii). So from my perspective, that was half my life ago that the 360 was at it's height in popularity, and more than a third of my life since they've been replaced. I'm not saying that consciously these are my reasons for justifying my opinion on the matter, but rather that these might be facts that subconsciously color my perspective without me even realizing until now, where I've put further thought into it. I mean, when the PS3 and Xbox 360 were released, I was still a happy person. When they peaked, life was pretty good. 

So yea, I'd say the PS3, 360 and Wii are pretty retro. 

That means a whole undiscovered history of certain consoles that were both current and retro at the same time .

Since my attempt at humour/satire failed I shall do what all would be comedians dread and hope never happens and that's having to explain your humor/ satire.

taking your statement to heart and using your being behind in graphics design and AI criteria I have experienced consoles that were brand new and retro the day of their release.

btw this is in no way related to my sense of self respect, but I was funny wasn't I ? and surely  you're man enough to admit to lacking a sense humour.

When second hand games for the console cost as much as brand new games for the current gen.

Ack, I guess the only retro console for me is Pong on Oscilloscope :/

You have a point though, I don't consider NES retro, nor record players. 8-track and tube amplifiers, that's retro to me. The stuff my grandparents used.

Gamecube/PS2/Xbox and everything prior feel "retro" to me.
I can still fire up a PS3/360/Wii game and while it may feel graphically dated its not far enough removed from modern game design to feel like a completely different era.