Can a trial court bar a person from serving as a witness because of the person's limited understanding or intelligence?

United States v. Shearer, 379 F.3d 453, 456 (7th Cir. 2004) (upholding trial court's admission of witnesses' testimony about accused's prior bad acts of selling display fireworks where such evidence was offered to prove accused's "intent to deal by demonstrating that [accused] engaged in...Evidence of a criminal or wrongful act apart from the act that at issue at trial Is not barred by the prohibition against circumstantial use of character if intent, knowledge, mistake, or accident is a legally-material factual issue, the opposing party suggests the non-existence of knowledge or urges mistake or accident as a defense, and evidence of another crime, wrong, or act is offered to prove the knowledge or the absence of mistake or accident by a criminal defendant or other person.

Pan American World Airways, Inc. v. Aetna Casualty & Surety Co., 368 F. Supp. 1098, 1104 n.5 (S.D.N.Y. 1973) (holding, in plaintiff airline company's action against defendant insurance carriers for insurance liability, that "reputation is acceptable as proof of....There is a hearsay exception for reputation in a community, arising before the controversy, as to boundaries of or customs affecting lands in the community, and reputation as to events of general history important to the community or State or nation in which located.

United States v. Koziy, 728 F.2d 1314, 1322 (11th Cir. 1984) (holding, in plaintiff US government's action against defendant for revocation of citizenship and cancellation of certificate of naturalization, that the trial....Federal Rule of Evidence 803(16) and comparable State rules create a hearsay exception for statements in an authenticated document that is more than a certain number of years old, typically twenty years.