More anecdata.

Lego from my youth, which was a hand-me down at the time, doesn't fit well with new lego. So it might be 40 years old, (which seems like a long time until you actually reach that age!)

I think it's more likely do to plastic aging than the original tolerances though.

To add even more - I was handed down Lego that belonged to my mom in the 60s, played with them through the 80s and 90s, and now my kids have them today. I wouldn’t be able to tell you which were hers and which were mine.