That is not true. The only numenorien who was an elf was Elros, Elrond's twin brother, who had elven blood, although he wasn't a "pure" elf. However, at the end of the First Era, it was given to the sons of Ëarendil(Elros and Elrond) the power to choose whether they would want to be elf or man. Elrond chose to be an elf, while his brother chose to be a man. Then, Elros became the first king of Númenor and lived for over 500 years.