Yes. Definitely possible.
I know some have done it. I haven't personally made it that far, but when I was young and had nothing better to do I spent a summer basically spam fighting the island trio and managed to get up to level 68. I honestly can't remember the exact game timer, and it wouldn't be particularly accurate anyway, since I spent a lot of time doing silly pointless time wasting stuff on the island anyway.
(My sister and I played a game called Hide the Coconut, where we would attack a random tree and then awkwardly walk into the dropped coconut to shove it under a bush or something to hide it, then the other one would have to figure out where it was hiding. Obviously this was clunky as hell and if you attacked another palm tree too many times or left the area it would erase the coconut so it had stupid limitations but eh, that's just sorta what you do when you are a bored kid).
Anyway, it definitely took me quite a lot of dedicated time. However, I was also playing with my journey starting at night, so that obviously affected level up speed. If you have a lot of time to waste it is actually a LOT of fun to have a super high level file at the start of the game because you can basically just troll play through everything. All the heartless in the beginning basically explode in one hit (up to a point anyway), I think Leon died in three hits (which made fainting after fighting him all the more infuriating). It's basically like playing through the game on god mode.
Sorry I can't give an exact hour count. I also can't check it as it was saved on my ps2 memory card of which I can't access any more.