Max for an attribute is 15. You can reset your attribute points at any point in the game by pressing
on the "Character" tab in the menu, however you probably won't have enough points for this achievement until you're level 8-10 (give or take, also dependent on stat bonuses from other things). So simply reset your points and dump 15 into any given attribute to unlock your achievement. Make a save beforehand if you wish to save some money, of course.
Edit: BRL mentions in the comments that temporary boost such as from items/totems invalidate the achievement, but I can confirm personally that permanent boosts (such as Kai's training) will work just fine, so make sure to either unequip any stat boosts or pick a stat to level that doesn't have any temporary boost.