|Darksol the Painbringer|
Also, to add on the whole "lacking limbs" issue, let's bring up an armless PC.
This poor guy got his arms tore off by breaking the law and was dealt the related consequences of the kingdom (probably stole something, so he lost in arms as a means to feel what it's like to be robbed of something precious, also done to make sure he can't steal again). Whatever, the point is now, this PC has zero arms, which means he cannot carry or use anything that absolutely requires hands/arms.
Would this PC be able to TWF? Maybe. But that depends on how it's executed.
If the PC is just a regular Fighter type (or a Rogue, to fit the flavor), he can't feasibly TWF. The TWF action requires you to declare which weapons you're using before you perform TWF, as per the FAQ regarding if attacking with two weapons instead of just one constitutes performing TWF, meaning he might be able to declare things like a Barbazu Beard, Armor Spikes, or Boot Blades.
As a concept, there's nothing wrong with it at first creation. But, the problem with this is the Armor Spikes FAQ. This FAQ states that you cannot use Armor Spikes with a Two-Handed Weapon, and this is enforced for two reasons:
1. When performing TWF, every weapon counts as requiring an arm/hand to use. If Armor Spikes do not normally require a hand to operate, and a FAQ disallows its use with something that requires two hands to operate, then the same can be made for trying to TWF with the likes of merely Unarmed Strikes (with your legs or head).
2. If your total statistical modifiers are greater than what you could normally accomplish (such as getting 2x Strength to damage in comparison to the standard 1.5x Strength), it becomes disqualified in the eyes of balance. This is an "unwritten" rule, one that I don't personally agree with (as well as many others), but it is a reason why this is disallowed, and was one of the reasons presented when the FAQ explanation was questioned.
Now, if this guy took levels in Monk so as to improve his Unarmed Skills, and acquired Flurry of Blows, there might be hope for him after all to effectively TWF, though that is still not the case with Manufactured Weapons, as Flurry of Blows requires Monk-specific weapons (which usually require hands to use), or can only be used with Unarmed Strikes.
Again, it's heavily enforced by FAQ that weapons require hands to use, and when subjects that don't require hands to use normally, they are still treated as requiring hands to use.