  In braneworld gravity models with a finite AdS curvature in the extra
dimension, the AdS/CFT correspondence leads to a prediction for the lifetime of
astrophysical black holes that is significantly smaller than the Hubble time,
for asymptotic curvatures that are consistent with current experiments. Using
the recent measurements of the position, three-dimensional spatial velocity,
and mass of the black hole XTE J1118+480, I calculate a lower limit on its
kinematic age of 11 Myr (95% confidence). This translates into an upper limit
for the asymptotic AdS curvature in the extra dimensions of 0.08 mm, which
significantly improves the limit obtained by table-top experiments of sub-mm
gravity.
