Perhaps I'll actually entertain this seriously.
I don't like this idea of "10/12/15/whatever year old games are retro." Even backwards generational counting is fickle and arbitrary. By these standards a slew of random PS2 games that are currently "modern" will be "retro" come next year. And/or the Wii will transform into a "retro system" once the NX hits. Makes no sense.
I consider games from the first, second, third, and fourth generations to be retro - along with certain fifth gen and even (early) sixth gen titles. Stuff like modern indie platformers found on Steam can be "retro" in style and substance but I prefer tags like "modern retro" to refer to games like that, to indicate that they're not actually from the days of old.
For me, the "cut-off" occurs where game design fundamentally changed in both technical and aesthetic applications - namely the integration of heavy narrative exposition into genres where it was previously lacking and the proliferation of 3D graphics, voice-acting, cutscenes, analog controls, and so forth. I've heard
Metal Gear Solid referred to as the "first modern game" - I'd take it a step further and say that a slew of others released in that era (
Final Fantasy VII,
Resident Evil, and so on) collectively comprise the "first modern games."
For the record, this is the viewpoint of someone who owns consoles ranging from the Odyssey up through the Wii U. I've noticed that many folks here who consider consoles like the PlayStation 2 to "retro" don't play games that predate it. On the flipside, I bet you can find old farts at AtariAge who'll claim that the crash of '83 marks the cut-off. It's a matter of perspective.
To swing back towards the original discussion of this thread, I wish there wasn't so much emphasis on whether someone is a "game collector" or not. I simply consider myself to be "into video games." Peoples' taste changes, life ebbs and flows; it doesn't always indicate a decreased appreciation for the hobby or medium.