Yes, that is actually an official rule. Though there is also a -2 penalty for using a weapon not meant for your size.
http://www.d20pfsrd.com/equipment---final/weapons
Also Page 144 of the Core Rulebook
Weapon Size
Every weapon has a size category. This designation indicates the size
of the creature for which the weapon was designed.
A weapon's size category isn't the same as its size as an object.
Instead, a weapon's size category is keyed to the size of the intended
wielder. In general, a light weapon is an object two size categories
smaller than the wielder, a one-handed weapon is an object one size
category smaller than the wielder, and a two-handed weapon is an
object of the same size category as the wielder.
Inappropriately Sized Weapons: A creature can't make optimum use of a
weapon that isn't properly sized for it. A cumulative –2 penalty
applies on attack rolls for each size category of difference between
the size of its intended wielder and the size of its actual wielder.
If the creature isn't proficient with the weapon, a –4 nonproficiency
penalty also applies.
The measure of how much effort it takes to use a weapon (whether the
weapon is designated as a light, one-handed, or two-handed weapon for
a particular wielder) is altered by one step for each size category of
difference between the wielder's size and the size of the creature for
which the weapon was designed. For example, a Small creature would
wield a Medium one-handed weapon as a two-handed weapon. If a weapon's
designation would be changed to something other than light,
one-handed, or two-handed by this alteration, the creature can't wield
the weapon at all.
Some DM's may handwave the -2 penalty for certain things. There really isn't that much of a difference between a shortspear meant for a medium character and a spear meant for a small character. An large creature's one-handed club is not that different from a medium creature's greatclub. That would be the place that a houserule would most likely come into play.
This dates from 3.5e (or earlier?) - the quote below is from the d20 SRD, and is the same in the PF SRD.
Double Weapons
Dire flails, dwarven urgroshes, gnome hooked hammers, orc double axes, quarterstaffs, and two-bladed swords are double weapons. A character can fight with both ends of a double weapon as if fighting with two weapons, but he or she incurs all the normal attack penalties associated with two-weapon combat, just as though the character were wielding a one-handed weapon and a light weapon.
The character can also choose to use a double weapon two handed, attacking with only one end of it. A creature wielding a double weapon in one hand can’t use it as a double weapon—only one end of the weapon can be used in any given round.
This is open to interpretation, but my opinion is that, as double weapons are already a special case that differ from the general rules for two-handed weapons, that WotC intended for them to be wieldable one-handed as this implies, as well as the explicitly stated two-handed or two-weapon methods.
However...
It appears that Paizo took a different view. There is a feat to specifically allow a character to wield a quarterstaff (a double weapon) one handed.
Quarterstaff Master (Combat)
You can wield a quarterstaff as either a two-handed or one-handed weapon.
Prerequisites: Weapon Focus (quarterstaff ), base attack bonus +5.
Benefit: By employing a number of different stances and techniques, you can wield a quarterstaff as a one-handed weapon. At the start of your turn, you decide whether or not you are going to wield the quarterstaff as a one-handed or two-handed weapon. When you wield it as a one-handed weapon, your other hand is free, and you cannot use the staff as a double weapon. You can take the feat Weapon Specialization in the quarterstaff even if you have no levels in fighter.
While the value of the feat is argued (due to the "WotC" interpretation of the double weapon rules), Paizo's official position is that you can't wield one handed without it.
Hey there folks,
You cannot normally use a double weapon in one hand unless it is sized smaller than you. This feat allows you to get around that restriction.
Jason Bulmahn
Lead Designer
Paizo Publishing
Best Answer
1. Less control: have them attack at disadvantage
Everyone has mentioned rolling with disadvantage and it makes a lot of sense especially when you consider the video from Icyfire’s answer demonstrating how a trained swordsman struggles when trying to use a two-handed weapon with one hand.
2. Less power: lower the dice by one type
There are several weapons that already have the versatile property, which means they’re supposed to be able to be wielded one-handed. These weapons still go down a dice type when you do this, though, to reflect the reduced power you have behind them.
3. Optional: Have pre-requisites
The thing with adding disadvantage alone is that, for instance, a gnome could wield a greataxe in the dark with just one hand, with another hand free for anything else, and despite the small size and lack of proficiency and everything else the only penalty they’d face is disadvantage. Have them successfully hide and it’s a straight roll!
Perhaps you could have a minimum strength requirement: only a character with a strength score above 15 can actually wield a two handed weapon with one hand; or maybe you homebrew a feat that allows this. In that case you might not even need to add all the other penalties...
4. Optional: Lose/alter the proficiency bonus
Losing the proficiency bonus entirely is a pretty intense penalty, especially at higher levels. It seems reasonable that if someone is proficient with a greatsword they’d be passable, at least, when using it one-handed. However, if you try with the other two elements and it still feels unbalanced, you could halve the proficiency bonus, for instance (rounding down as you do with everything in 5e.)