21st Century Assistive Technology Act This bill reauthorizes through FY2024, modifies the funding allocations for, and makes administrative and other changes to certain grants and programs to increase access to assistive technology devices and assistive technology services for individuals with disabilities. These devices include any item, piece of equipment, or system that is used to maintain or improve the functional capabilities of individuals with disabilities (e.g., wheelchairs, hearing aids, or screen readers and computer software), and an assistive technology service is a service that directly assists an individual with a disability with selecting or using such devices, including by evaluating the individual's needs or expanding access to such devices and technology. Among other changes, the bill revises requirements for certain technical assistance to support grant recipients with data collection and other activities, increases requirements for collaboration between agencies that are implementing certain state grants for assistive technology and other state agencies that receive other sources of federal funding for this technology, and includes older adults more explicitly in the scope of particular programs.