  We fit the upper main sequence of the Praesepe and Hyades open clusters using
stellar models with and without rotation. When neglecting rotation, we find
that no single isochrone can fit the entire upper main sequence at the
clusters' spectroscopic metallicity: more massive stars appear, at high
significance, to be younger than less massive stars. This discrepancy is
consistent with earlier studies, but vanishes when including stellar rotation.
The entire upper main sequence of both clusters is very well-fit by a
distribution of 800 Myr-old stars with the spectroscopically measured
[Fe/H]=0.12. The increase over the consensus age of ~600-650 Myr is due both to
the revised Solar metallicity (from $Z_\odot \approx 0.02$ to $Z_\odot \approx
0.014$) and to the lengthening of main sequence lifetimes and increase in
luminosities with rapid rotation. Our results show that rotation can remove the
need for large age spreads in intermediate age clusters, and that these
clusters may be significantly older than is commonly accepted. A
Hyades/Praesepe age of ~800 Myr would also require a recalibration of
rotation/activity age indicators.
