  Tight binaries discovered in young, nearby associations, with known
distances, are ideal targets to provide dynamical mass measurements to test the
physics of evolutionary models at young ages and very low masses. We report for
the first time the binarity of TWA22, possible new dynamical calibrator for
evolutionary models at young ages. Based on an accurate trigonometric distance
(17.53 +- 0.21 pc) determination, we infer a total dynamical mass of 220 +- 21
MJup for the system. From the resolved near-infrared integral-field
spectroscopy, we find an effective temperature Teff=2900+200-200 K for TWA22 A
and Teff=2900+200-100 K for TWA22 B and surface gravities between 4.0 and 5.5
dex. From our photometry and a M6 +- 1 spectral type for both components, we
find luminosities of log(L/Lsun)=-2.11 +- 0.13 dex and log(L/Lsun)=-2.30 +-
0.16 dex for TWA22 A and B respectively. By comparing these parameters with
evolutionary models, we question the age and the multiplicity of this system.
We also discuss a possible underestimation of the mass predicted by
evolutionary models for young stars close to the substellar boundary.
