However, passport cards are not valid for international air travel, meaning you must also hold a passport book if you plan to travel out of the country by plane. Adult Card Validity Any United States citizen over the age of 16 can apply for an adult passport card. Like passport books, adult passport cards remain valid for 10 years from the date of issue. The date your passport card was issued is printed on the front of the card along with the expiry date, making it easy to check how much validity is left. Children’s Card Validity. Children’s passport cards are only valid for five years. Again, this is the same validity period applied to the traditional passport book.