  We have investigated a group of stars known to have low chromospheric ages,
but high kinematical ages. Isochrone, chemical and lithium ages are estimated
for them. The majority of stars in this group show lithium abundances much
smaller than expected for their chromospheric ages, which is interpreted as an
indication of their old age. Radial velocity measurements in the literature
also show that they are not close binaries. The results suggest that they can
be formed from the coalescence of short-period binaries. Coalescence rates,
calculated taking into account several observational data and a maximum
theoretical time scale for contact, in a short-period pair, predict a number of
coalesced stars similar to what we have found in the solar neighbourhood.
