Okay, I heard something saying that you can get to level 100. that may not be the first Kingdom Hearts, but still...
I thought I would tell you the quick way I use to leveling up. The Hades world cup at the Colosseum. Do it alone, together, or time attack... From begginging to end. I was level 71 or 70 when I went at it alone (Ha ha ha... Took me so long) But when I was done i was about level 74. Then I left and got another level up at a random place. I could have been level 73 and got a level up to 74, so don't think your leaving Hades cup and going to be level 75!