Stellar age is a key fundamental property for understanding the history, evolution, and future of stellar populations, the Milky Way, and exoplanets. However, age is extremely difficult to measure for individual stars. Low-mass stars, or M dwarfs, are the most numerous stars in the Galaxy, they have lifetimes longer than the current age of the Universe, and are likely to host the majority of Earth-like exoplanets. For this reason, these main sequence stars are ideal for studying the Milky Way and exoplanets properties in a wide range of ages. Ages of M dwarfs are especially difficult to estimate because methods used for solar-type stars break down as lower mass objects become fully convective. I want to build a robust Bayesian algorithm to infer ages of M dwarfs from three age indicators: 1) Position in the color-magnitude diagram; 2) Magnetic activity, as indicated by Hα equivalent widths; 3) Full kinematics, taking advantage of Gaia DR2. I will present the age-calibrations I did of these age indicators, including the age-activity relation for Hα. I will show the results we obtained from our calibration of the age-activity relation, which indicates that Hα equivalent widths decrease with age. I will also explain how we are going to use this relation to obtain precise estimation of M dwarf ages.