  We describe Chandra/ACIS-I observations of the massive ~ 13--14 Myr-old
cluster, h Persei, part of the famous Double Cluster (h and chi Persei) in
Perseus. Combining the list of Chandra-detected sources with new optical/IR
photometry and optical spectroscopy reveals ~ 165 X-ray bright stars with V <
23. Roughly 142 have optical magnitudes and colors consistent with cluster
membership. The observed distribution of Lx peaks at Lx ~ 10^30.3 ergs/s and
likely traces the bright edge of a far larger population of ~ 0.4--2 Msun X-ray
active stars. From a short list of X-ray active stars with IRAC 8 micron excess
from warm, terrestrial-zone dust, we derive a maximum X-ray flux incident on
forming terrestrial planets. Although there is no correlation between X-ray
activity and IRAC excess, the fractional X-ray luminosity correlates with
optical colors and spectral type. By comparing the distribution of Lx/L* vs.
spectral type and V-I in h Per with results for other 1--100 Myr-old clusters,
we show that stars slightly more massive than the Sun (> 1.5 Msun) fall out of
X-ray saturation by ~ 10--15 Myr. Changes in stellar structure for > 1.5 Msun
stars likely play an important role in this decline of X-ray emission.
