I wouldn't say it hasn't aged but there is a reason Citizen Kane is often cited as the greatest film of all time. If you changed Charles Foster Kane's profession from newspaper tycoon to social media magnate the story would take on a whole new relevance.
It was a very provocative film in its time. William Randolph Hearst forbid any of his newspapers to even mention it. Not surprising as it's critical undertone was aimed squarely at him and his peers.
Edit: Sunset Boulevard is another oldie but goody.
I think the humor of Casablanca ultimately makes it age just a bit better than Citizen Kane, but they really are both phenomenal movies.
Oh I'd definitely second 12 Angry Men. I'd also add Dr. Strangelove
Young Frankenstein
I only discovered it about 15 years ago but it's been one of my favourite films since and I think it stands up remarkably well. The jokes are all still hillarious and the acting, camera work and set design is a lot of fun to watch.
It's technically B&W, but that was a stylistic choice to make it look like prior monster movies. It's not nearly as old as most B&W films that were made that way due to the lack or expense of color technology.
I'm not 100% what you mean by 'not aged', but I was rewatching The Thin Man (1934) the other day, and that film still makes me laugh out loud. It's a great mystery/comedy.
The Artist.
Considering its youngness, i wouldn't consider its non-aging as "surprising".
Seven Samurai still holds up. Also, the original Godzilla.
I came into this thread to say 12 Angry Men, but because OP already named it I'll say A Face in the Crowd. It stars Andy Griffith as an egomanic drunk who finds fame as a radio star and later TV personality, and uses it to leverage the public opinion to the point where he himself is meeting with high level government officials. It's a chilling chronicle of one man's descent into madness and eventual self-destruction by his own doing, all for a taste of fame and power. Lonesome Rhodes is a near opposite character to that of Sherriff Andy Taylor; this movie really opened my eyes to Andy Griffith's incredible range.
