I like to see “old” as a spectrum influenced by the current time period and technology rather than a binary. A movie from the 2000s would have come out 20+ years ago and a lot of the filming techniques, pacing, plot, and special effects reflect that. So that’s an old film time wise even if it’s stylistically more similar than old classics from the 70s or 50s.
It’s relative. If the discussion is focusing on movies made in the last five years, I’d probably consider anything 2012 or older “old”. If the discussion is focused on 90s movies, then only stuff you’d see on Turner Classic Movies counts as old. And if the discussion is focused on TCM movies? Then only silent films count as old. At least, that’s my take.