I found that if you get that enemy skill where all those missiles come out of your back (you can get it from enemies near midgar) and go to the Mithril mines (go to the chamer in the upper left of where you met the turks) you can get every one's limit break if you so desire early in the game. Aeris, Cloud, Tifa (tifa's limit break is wicked if you get it up early)

I never had problems getting any limit break for any character at any time during the game. Its just a pain in the ass killing 80 monsters straight.