  A reliable age estimation for the field brown dwarf LP 944-20 is accomplished
through the analysis of its kinematic properties. The space velocities of this
star strongly suggest its membership in the so-called Castor moving group. LP
944-20 can be sensibly assumed to have the group's age, which is estimated to
be ~320 Myr, and metal content, which is found to be roughly solar. With these
new constrains and the available photometry and lithium abundance, current
brown dwarf models are put to a test. Using the IR magnitudes and the lithium
diagnostics, the models are able to provide a reasonable description of the
brown dwarf's properties (to within a few sigma) but yield an age which is
roughly 50% larger than our estimate. Possible reasons for this discrepancy are
discussed.
