Recently, very robust universal properties were shown to arise in one-dimensional growth processes with local stochastic rules, leading to the Kardar-Parisi-Zhang universality class. Yet it has remained essentially unknown how fluctuations in these systems correlate at different times. Here we derive quantitative predictions for the universal form of the two-time aging dynamics of growing interfaces and we show from first principles the breaking of ergodicity that the KPZ time evolution exhibits. We provide corroborating experimental observations on a turbulent liquid crystal system, as well as a numerical simulation of the Eden model, and we demonstrate the universality of our predictions. These results may give insight into memory effects in a broader class of far-from-equilibrium systems.Introduction. Non-equilibrium dynamics is ubiquitous in nature, and takes diverse forms, such as avalanche motion in magnets and vortex lines [1, 2] ultraslow relaxation in glasses [3, 4], unitary evolution towards thermalization in isolated quantum systems [5], coarsening in phase ordering kinetics [6], and flocking in living matter [7]. Prominent examples are growth phenomena, which abound in physics [8, 9, 11, 12], biology [8, 13,14], and beyond [15]. As some of these systems try to reach local equilibrium or stationarity, a great variety of behaviors can occur, such as aging dynamics and memory of past evolution [1, 4, 6,16]. How universal and generic are these behaviors is a fundamental question [16].One important example of growth arises when a stable phase of a generic system expands into a non-stable (or meta-stable) one, in presence of noise. While spreading, the interface separating the two phases develops many non-trivial geometric and statistical features. A universal behavior then emerges, unifying many growth phenomena into a few universality classes, irrespective of their microscopic details. The most generic one, for local growth rules, is the celebrated Kardar-Parisi-Zhang (KPZ) class, now substantiated by many experimental examples, such as growing turbulence of liquid crystal [9][10][11], propagating chemical fronts [15], paper combustion [12] and bacteria colony growth [13]. For one-dimensional interfaces growing in a plane, as studied in many experiments, it is characterized by the following KPZ equation [17]: