I usually beat these games between 60 and 70 hours, and I usually do the majority of the sidequest, get rare weapons, etc. I don't see how some people can put so much time into some of these games. I can see if you are a completionist and are trying to max stats and get every item and such, but otherwise I completely agree with Sheena that it is almost a waste of time to play for 100+ hours. For example, in Final Fantasy IX, you can do just about everything in 70 hours. The only thing you probably wouldn't be able to do is get to level 99, which I don't understand why it would matter if you can beat every boss when your characters' levels are in their 40s/50s.

I think the only Final Fantasy game that is taking really long for me is Final Fantasy XII, and that is because I've been level grinding for 20-30 hours now. This game will be one of the few games that take me more than 100 hours to complete.

If you are just trying to beat the game, the average would probably be 40-50 hours.