I do not think levels are a crucial factor while playing FFVII, since if you have a correct stratagy, then you could beat most bosses, without the appropriate levels.

I think I was in my early 20's, but I did not have a problem throughout the game, even when I defeated Emerald and Ruby weapon at level 60. I despise training my characters, and I never set time aside to train them, but I guess if you want a non-challenging game then you could train a lot, but I don't find it neccessary.