Every persona starts with 10 stats at level 1, each time they level up they receive 3 stat points that are randomly distributed. At the max level, a Persona will have 304 stats points in total. This means that it’s impossible to max every stat. For a Persona to max out 3 stats (we’re assuming maxed means 94 points because there’s a ranged weapon that grants +5 to all stats), that Persona has to start at level 5 or less. For a Persona to max 2 stats (assuming 0 points in that stat to begin with) the level would be 36. To max one stat from 0, highest level would be 67. For 2 and 3 stat maxing, the highest level cap will be different since realistically that Persona will already have several points in those stats you want to max out.
There is a way to manipulate your stat gains, but it’ll take some time and planning and lots of Yen.
Using gallows sacrifice allows you to see which stats will increase when you level up, this is shown by the gold bars over the Persona’s stats. If you don’t get the spread you’re looking for, you can back out of the menu and back in again for a new spread. It’s possible to land on +3 for one stat per level up. How much experience you get depends on the Persona you’re sacrificing, it’s easiest to control the stat gains when going up one level at a time. You’ll have some leeway if you’re leveling up a Persona with the aim to max 3 stats, for example Strength, Agility and Endurance. This can get very expensive as you’ll have to keep pulling Personas out of the compendium to strengthen the ones you want.
You can find a recap on what stats do here. Generally for magic users aim for maxed magic and agility. For strength users aim for maxed strength and agility. You’ll probably want endurance as a third stat for defense, since magic can’t crit luck doesn’t really help magic users. A mix of luck and endurance will be nice for strength Personas.