The ages of cool main-sequence stars are notoriously difficult to measure, however, in the era of Gaia, the 3D velocities of stars have the potential to reveal their kinematic ages. In particular, the established relationship between stellar age and vertical velocity dispersion for stars in the Solar neighborhood provides an opportunity to statistically age-date stars. Kinematic stellar ages are particularly useful for calibrating alternative empirical dating methods. For example, gyrochronology, the method of inferring the age of a main-sequence star from its rotation period, shows great promise as a dating method, however it is still poorly calibrated for K and M dwarfs. Kinematic ages could provide the calibration sample needed to fully calibrate gyrochronology, opening up a new pathway for dating the coolest and oldest stars in the Milky Way. In this talk, I describe how we can use kinematic ages to study stellar evolution, and potentially even to calibrate empirical age-rotation relations for cool stars. I will also describe how we infer 3D stellar velocities for Kepler targets using Gaia positions, parallaxes and proper motions alone, marginalizing over missing radial velocity measurements.