Is there objective evidence for free will?

After doing some research on free will and determinism, the existence of free will seems pretty unlikely to me -- even though the thought of free will is comforting. An argument often used to refute determinism is that the determinist says that we should accept determinism, since on his view, he only advocates determinism because he's determined. That seems unsatisfying, however, since that doesn't prove the existence of free will. Also, even if each person can say of himself, "I have free will," how do you determine whether others have free will? How would you know whether a toddler, a teenager, a person with a brain tumor, or a person with dementia has free will or not?