  We present resolved NACO photometry of the close binary AB Dor B in H- and
Ks-band. AB Dor B is itself known to be a wide binary companion to AB Dor A,
which in turn has a very low-mass close companion named AB Dor C. These four
known components make up the young and dynamically interesting system AB Dor,
which will likely become a benchmark system for calibrating theoretical
pre-main sequence evolutionary mass tracks for low-mass stars. However, for
this purpose the actual age has to be known, and this subject has been a matter
of discussion in the recent scientific literature. We compare our resolved
photometry of AB Dor Ba and Bb with theoretical and empirical isochrones in
order to constrain the age of the system. This leads to an age estimate of
about 50 to 100 Myr. We discuss the implications of such an age range for the
case of AB Dor C, and compare with other results in the literature.
