  We report initial results from our long term search using precision radial
velocities for planetary-mass companions located within a few AU of stars
younger than the Sun. Based on a sample of >150 stars, we define a floor in the
radial velocity scatter, sigma_RV, as a function of the chromospheric activity
level R'_{HK}. This lower bound to the jitter, which increases with increasing
stellar activity, sets the minimum planet mass that could be detected. Adopting
a median activity-age relationship reveals the astrophysical limits to planet
masses discernable via radial velocity monitoring, as a function of stellar
age. Considering solar-mass primaries having the mean jitter-activity level,
when they are younger than 100 / 300 / 1000 Myr, the stochastic jitter
component in radial velocity measurements restricts detectable companion masses
to > 0.3 / 0.2 / 0.1 M_Jupiter. These numbers require a large number -- several
tens -- of radial velocity observations taken over a time frame longer than the
orbital period. Lower companion mass limits can be achieved for stars with less
than the mean jitter and/or with an increased number of observations.
