We derive a new age for the γ2 Velorum binary by comparing recent observations to our set of binary models. We find that it is very unlikely that the stars have not interacted, which implies that previous estimates of the age from single-star models of 3.5 ± 0.4 Myr are incorrect. We prefer an older age of 5.5 ± 1 Myr that agrees with the age of other lower mass stars in the Vela OB association. We also find that our favoured binary model shows the components of the binary have interacted in a Case B, post-main-sequence, mass-transfer event. During the mass-transfer event, the envelopes of both components are radiative and therefore the damping of tidal forces is relatively weak. This explains why the binary is still eccentric after mass transfer.