Stats in this game are based on the job you have when you gain a level. Each job has its own growth amounts, and its own base starter stats. So if you start as an Archer and gain a few levels as an Archer, you're going to get a lot of Archer stats. So when you switch to White Mage, you won't have nearly as high magic as someone who started White Mage and leveled as it.

That said, if you pick the right jobs to level (and get some luck, as each job actually has a growth "range" of about 3 points per stat), you can actually max several stats with enough persistence. I don't recommend it unless you are as insane as I am.

So, for stats, you need to determine if you want to spread stats out among several jobs for well rounded characters, or focus on specific jobs to optimize them.