Just What is "Retro"?

So I'm thumbing through the latest issue of Retro Gamer when I come to the letter section. A reader was disappointed with the N64 collector's guide segment from a few issues back. That didn't really come as too much of a surprise to me. Not saying it was bad or anything, but what really stuck out to me was his opinion of the N64 being thought of as a retro platform. He said the the N64 was bout "as retro as the Xbox 360."

I'm a huge old-school gamer but by no means do I claim to be an expert on the subject. Is there some sort of expatriation date on a console's life that officially makes it part of the retro club? Are retro systems only retro because they use blocky visuals, sprites and not polygons? The N64 is hardly a new system. It hit the streets in 1996. The system will be turning 15 years old this year (in June for Japan, September for the USA, and March of 1997 in Europe). Old girl is pushing two decades old. She hasn't been a spring chicken for quite some time now. What about the PlayStation? It's just a year or two older than it's 64-bit rival. Is it also not retro because it didn't debut in the days of the Commodore 64 or NES?

Maybe I'm reading far too much into someone's thoughts of mid-nineties systems being thought of as retro but I think it's safe to say that not everyone's opinions of retro are the same. This isn't the first time this topic has crossed my mind, but it's the first time I've given it as much though.

In the late 1990s and early 2000s, the SNES and Genesis were retro in my eyes. These systems could have been shinny and new to others. I picked up my Sega Saturn in 2006 but it originally came out in 1995. It was already a piece of gaming history in my mind. I view the N64 and PlaySation the same way, of course, that's just me. I honestly can't name all of the specifics of what I think makes games and game consoles old, but personally, I wouldn't say game consoles that are nearly 20 years old are new. What's your take?