The 21st Century American Atomic Energy Age Act aims to accelerate the development and deployment of small modular nuclear reactors in the United States while reducing dependence on Russian nuclear fuel. The bill establishes a new Office of Nuclear, Economic, Environmental, and National Security within the Nuclear Regulatory Commission to streamline licensing for innovative reactor designs and evaluate their economic and national security benefits. It prohibits the use of Russian-produced nuclear fuel in small modular reactors starting 90 days after enactment and requires the Secretary of Commerce to create compliance procedures within 183 days. The bill also extends liability protections for nuclear operators under the Price-Anderson Act from 2025 to 2045 and directs the secretaries of Energy, Homeland Security, and Defense to identify critical infrastructure that could benefit from onsite nuclear power generation. The legislation authorizes unspecified funding necessary to implement these provisions and takes effect 120 days after enactment.