Speaking as a massive Final Fantasy fan, I don't think the first one has aged particularly well. It's really tedious; battles take way too long even with battle speed set to max, and the random encounter rate is insane. It makes traveling anywhere a complete slog, especially when you get to the point where nothing on the overworld challenges you anymore. There's no equivalent of Holy Protection from Dragon Quest where you can make the low-level encounters fuck off; having to wade through a sea of goblins that pose zero threat feels like a waste of time. And the level scaling feels fucked in the early game. There's a reason people abuse the Peninsula of Power, and it's because the early monsters give so little experience that it takes an eternity just to level up to where you can feasibly tackle the Marsh Cave and the Cavern of Earth. When you get the canoe, the grind and balancing get better, but the grind in the early game is unbearable.
It's not even because FF1 is an old JRPG, because I played through the first three Dragon Quests and Mother 1 and had a much better time with those games. FF1 just plain lacks a lot of the polish, mechanics, and interesting worldbuilding that make those other games enjoyable.
