National Senior Investor Initiative Act of 2018 or the Senior Security Act of 2018 This bill amends the Securities Exchange Act of 1934 to establish the Senior Investor Taskforce within the Securities and Exchange Commission. The taskforce must report on topics relating to investors over the age of 65, including industry trends and serious issues impacting such investors, and make recommendations for legislative or regulatory actions to address problems encountered by senior investors. The Government Accountability Office must report on the costs of the financial exploitation of senior citizens.