A Revised Age for Upper Scorpius and The Star-Formation History Among
  the F-Type Members of the Scorpius-Centaurus OB Association
  We present an analysis of the ages and star-formation history of the F-type
stars in the Upper Scorpius (US), Upper Centaurus-Lupus (UCL) and Lower
Centaurus-Crux (LCC) subgroups of Scorpius-Centaurus. We find that 1) our
empirical isochrones are consistent with the previously published age-rank of
the Sco-Cen subgroups, 2) LCC and UCL appear to reach the main sequence turn-on
at spectral types ~F4 and ~F2, respectively. An analysis of the A-type stars
shows US reaching the main sequence at about spectral type ~A3. 3) The median
ages for the pre-main sequence members of UCL and LCC are 16 Myr and 17 Myr,
respectively, in agreement with previous studies, however we find that 4) Upper
Sco is much older than previously thought. The luminosities of the F-type stars
in US are typically a factor of ~2.5 less luminous than predicted for a 5 Myr
old population for four sets of evolutionary tracks. We reexamine the
evolutionary state and isochronal ages for the B-, A-, and G-type Upper Sco
members, and the evolved M supergiant Antares, and estimate a revised mean age
for Upper Sco of 11+/-1+/-2 Myr (statistical, systematic). Using radial
velocities and Hipparcos parallaxes we calculate a lower limit on the kinematic
expansion age for Upper Sco of >10.5 Myr (99% confidence). However, the data
are statistically consistent with no expansion. We reevaluate the inferred
masses for the known substellar companions in Upper Sco using the revised age.
Specifically, we estimate the mass of 1RXS J1609-2105b to be 14^{+2}_{-3} Mjup,
suggesting that it is a brown dwarf rather than a planet. Finally, we find the
fraction of F-type stars exhibiting Ha emission and/or a K-band excess
consistent with accretion to be 0/17 (<19%; 95% C.L.) in US at ~11 Myr, while
UCL has 1/41 (2^{+5}_{-1}%; 68% C.L.) accretors and LCC has 1/50 (2^{+4}_{-1}%;
68% C.L.) accretors at ~16 Myr and ~17 Myr, respectively. [Abridged]
