In philosophy, free will gets linked to choice. The two ends of the spectrum, of choice, are free will and determinism respectively. In reality, we live within a state of being that is a mixture of both concepts. We as people are composed from partly a result of our heredity and partly a result of our environment, which are both mostly out of our control. But its possible to have no choice whatsoever in our circumstances and genetics and still have at least a portion of free will - in how we think, what we say, etc. The exercise of free will does not require a change in either circumstances or genetics in order to be free will. The real question is whether we can prove it or not. Who is to say that a decision I just made is me, my genetics or my environment?
Philosophically I think every person is unique and they represent that third option, in addition to genetics and environment. Its a belief of mine. The concept of a unique "I" existing is consistent with other aspects of life.
The constitution, for instance, contains the line "life, liberty and the pursuit of happiness" as unalienable rights. Does a paraplegic have those rights, too, even though they can't move? Does a blind person have them even though they can't see? They can't make certain choices, like walking or seeing, but I'd argue that they still have those rights and can still exercise free will. It just happens to be a restricted form of free will, same as everybody else in the whole world has for one reason or the other.