Saying 90s anime is "not old" compared to 70s/80s anime in 2024 is like saying the High Middle Ages aren't part of the Middle Ages in general.
So, just for fun, I recommend OG Hokuto no Ken (Fist of the North Star), from '86. 'Tis the anime that makes grown men shed the manliest of tears.
Moving on, more "recent" recommendations:
#. Planetes (2004) - Possibly the most realistic and most engaging slice-of-life near-future sci-fi in all of existence that's about the life of orbital garbage collectors. ('cause Kessler Syndrome, you know.)
#. Kurosu Anju Tenshi to Ryū no Rondo (Cross Ange: Rondo of Angels and Dragons; 2014) - Girl power, mechas, dragons, eco fiction, awesome music, the works! The main villain is a bit weak in terms of writing, but everything else is awesomesauce.
#. Tengen Toppa Gurren Lagann (Gurren Lagann; 2008) - The definitive "Humanity, fuck yeah!!!" story that all others are compared against. Has some plot holes here and there, but the pacing, breakneck tempo, kickass OST, and general absurdity of it all make up for it in spades. (It's also the origin place of the "unsheathing the sword" meme)
#. Kobayashi-san Chi no Meidoragon (Miss Kobayashi's Dragon Maid; 2017-) - Yes, on the surface it's a silly slice-of-life with plenty of fanservice and over-the-top sexual innuendos, but it has a surprising amount of philosophical depth, thanks to the juxtapositions of human and draconic worldviews. It's currently an ongoing series, but S1 and S2 that are out so far can provide much food for thought, if viewed with the appropriate mindset. Also, the music is very good.
There's many more, but other people have already made some cool recs, which I won't repeat here. Bear in mind, what I've shared I consider top of the top, not only in terms of anime, but in terms of stories in general, regardless of medium. This is art that causes one to grow, not just be entertained.
Also, part of the fun is to discover your own favorite all-timers. Anime is so vast in terms of content, it's almost silly.
Regards,
Sagacious
PS. Oh, and I'm serious about Hokuto no Ken. It's great. It has many, many filler episodes, though, but the good episodes more than make up for the rest. Rest in peace, kung-fu Jesus.