  The vast majority of stars in the nearby stellar neighborhood are M dwarfs.
Their low masses and luminosities result in slow rates of nuclear evolution and
minimal changes to the star's observable properties, even along astronomical
timescales. However, they possess relatively powerful magnetic dynamos and
resulting X-ray to UV activity, compared to their bolometric luminosities. This
magnetic activity does undergo an observable decline over time, making it an
important potential age determinant for M dwarfs. Observing this activity is
important for studying the outer atmospheres of these stars, but also for
comparing the behaviors of different spectral type subsets of M dwarfs, e.g.,
those with partially vs. fully convective interiors. Beyond stellar
astrophysics, understanding the X-ray to UV activity of M dwarfs over time is
also important for studying the atmospheres and habitability of any hosted
exoplanets. Earth-sized exoplanets, in particular, are more commonly found
orbiting M dwarfs than any other stellar type, and thermal escape (driven by
the M dwarf X-ray to UV activity) is believed to be the dominant atmospheric
loss mechanism for these planets. Utilizing recently calibrated M dwarf
age-rotation relationships, also constructed as part of the $\textit{Living
with a Red Dwarf}$ program (Engle & Guinan 2023), we have analyzed the
evolution of M dwarf activity over time, in terms of coronal (X-ray),
chromospheric (Lyman-$\alpha$, and Ca II), and overall X--UV (5--1700 Angstrom)
emissions. The activity-age relationships presented here will be useful for
studying exoplanet habitability and atmospheric loss, but also for studying the
different dynamo and outer atmospheric heating mechanisms at work in M dwarfs.
