Fan theories are controversial, and this Aladdin theory is no exception. But fan theories, much like the original works they're based upon, require you to suspend your disbelief and just enjoy the ride.
In one scene, Genie calls Al’s clothes “So 3rd century”.
Genie was trapped for 10,000 years, so there is no way he could know of the fashion trends which have happened whilst he was in the lamp. Which means at the latest Genie could have been trapped in the lamp during the 3rd century.
If he spent 10,000 years in there, it is then AT LEAST the year 10,300AD when he gets out.
A post-apocalyptic world where only Arabic (and some Greek) culture survived. It has been so long that the name “Arabia” has been corrupted to “Agrabah”.
Amazing technological marvels left behind by the previous civilization, like flying carpets or genetically engineered parrots which can comprehend human speech instead of just mimicking it, are taken for granted by locals or considered “Magic”. The Genie proves this by making impressions of ancient, long-dead celebrities like Groucho Marx, Jack Nicholson, etc."
Wow. What an insightful take on a longtime classic, and one of my personal favorite Disney films.