The judge or judges regularly presiding in the circuit court of each county and city shall annually, in the month of June, July, or August, select from citizens of the county or city at least 60 persons and not more than 120 persons 18 years of age or over, of honesty, intelligence, impartiality, and good demeanor and suitable in all respects to serve as grand jurors, who, except as hereinafter provided, shall be the grand jurors for the county or city from which they are selected for the next 12 months. The judge or judges making the selection shall at once furnish to the clerk of the circuit court a list of those selected for that county or city. The clerk, not more than 20 days before the commencement of each term of his court at which a regular grand jury is required, shall issue a venire facias to the sheriff of his county or city, commanding him to summon not less than five nor more than nine of the persons selected as aforesaid (the number to be designated by the judge of the court by an order entered of record) to be named in the writ to appear on the first day of the court to serve as grand jurors. Those persons who are to be summoned shall be randomly selected but no such person shall be required to appear more than once until all the others have been summoned once, nor more than twice until the others have been twice summoned, and so on. The Circuit Court of James City County, or the judge thereof in vacation, shall select the grand jurors for each court from such county and the City of Williamsburg in such proportion from each as he may think proper. Any person who has legal custody of and is responsible for a child 16 years of age or younger or a person having a mental or physical impairment requiring continuous care during normal court hours shall be excused from jury service upon his request.