Context :

Aims : We have estimated the age of the young moving group TW Hydrae Association , a cohort of a few dozen stars and brown dwarfs located near the Sun which share the same kinematic properties and , presumably , the same origin and age .

Methods : The chronology has been determined by analyzing different properties ( magnitudes , colors , activity , lithium ) of its members and comparing them with several well-known star forming regions and open clusters , as well as theoretical models .
In addition , by using medium-resolution optical spectra of two M8 members of the association ( 2M1139 and 2M1207 –an accreting brown dwarf with a planetary mass companion ) , we have derived spectral types and measured H \alpha and lithium equivalent widths .
We have also estimated their effective temperature and gravity , which were used to produce an independent age estimation for these two brown dwarfs .
We have also collected spectra of 2M1315 , a candidate member with a L5 spectral type and measured its H \alpha equivalent width .

Results : Our age estimate for the association , 10 ^ { +10 } _ { -7 } Myr , agrees with previous values cited in the literature .
In the case of the two brown dwarfs , we have derived an age of 15 ^ { +15 } _ { -10 } Myr , which also agree with our estimate for the whole group .

Conclusions : We compared our results with recent articles published on the same subject using other techniques , and discuss the limits of the age-dating techniques .