We present a new model of real-time periodic distributed asynchronous computation in which information flows through sequences of periodic tasks, where task inputs are obtained by sampling other task's outputs as well as sampling the environment. We introduce a metric for end-to-end timing called the age of an output, which is the time since the external inputs on which an output value is based were sampled. We present some bounds on age scheduling efficiency, reduce the problem of finding a feasible distributed age schedule to finding a solution for a system of nonlinear constraints, and discuss use of a commercial solver to find a solution to a large problem derived from a real-world system.