With the age for voting rights being lowered this summer, 18-year-olds are gathering attention. In most countries, 18 is the age of adulthood. Are Japanese 18-year-olds adultlike or childish compared to foreign 18-year-olds? We survey foreign and Japanese high schoolers living in Japan about topics such as money, family, and romance and compare. We discuss with foreigners with the unique answer as the doorway. Are Japanese 18-year-olds cools? We investigate from the perspective of foreigners.