  We present a study of age-related spectral signatures observed in 25 young
low-mass objects that we have previously determined as possible kinematic
members of five young moving groups: the Local Association (Pleiades moving
group, age=20 - 150 Myr), the Ursa Major group (Sirius supercluster, age=300
Myr), the Hyades supercluster (age=600 Myr), IC 2391 supercluster (age=35--55
Myr) and the Castor moving group (age=200 Myr).
  In this paper we characterize the spectral properties of observed high or low
resolution spectra of our kinematic members by fitting theoretical spectral
distributions.
  We study signatures of youth, such as lithium {\sc i} 6708 \AA, H$\alpha$
emission and other age-sensitive spectroscopic signatures in order to confirm
the kinematic memberships through age constraints.
  We find that 21 ($84\%$) targets show spectroscopic signatures of youth in
agreement with the age ranges of the moving group to which membership is
implied. For two further objects, age-related constraints remain difficult to
determine from our analysis. In addition, we confirm two moving group kinematic
candidates as brown dwarfs.
