Where do you draw the line that games become too old to interest you?
If you had to point a year where games older than that are a rare exception for you and more than 95% of what you play is newer, when would that be?

For me it's 1988.
1990 & 1991 are pretty much my favorite years of video games ever and 1989 is still full of lots of good stuff, but 1988 and before it's very rare for me to play.

This is mostly based on PC gaming. But also on consoles I'm going 16-bit or late 8-bit in my oldest retrogaming.

You could argue I have some favorites from 1988 and even more so 1987, so fair alternative would be 1986, beyond which there's really almost nothing I've seriously played.

I own Atari 2600 games from the 70s and enjoyed them immensely.