Go to any player's details page. The one with age, height, exp to next level and whatever. You can see the last one says "max level cap". This is the max level the player can reach with limit breaking.
So for scouted players, their max level cap is 30. For agent and special agent players, theirs is 50 and 60 respectively, which is higher than 31.
They kinda confused everyone, myself included at first, by saying things like "31 and above", when no one's max level cap is 31 or 32 and so on.
Basically all scouted players will be level 30 and then you can continue to level them up after that to their max, while all other players will be at their max level immediately.