We study the equilibrium and dynamical properties of a spherical version of the frustrated Blume-Emery-Griffiths model at mean field level for attractive particle-particle coupling (K>0). Beyond a second order transition line from a paramagnetic to a (replica symmetric) spin glass phase, the density-temperature phase diagram is characterized by a tricritical point from which, interestingly, a first order transition line starts with coexistence of the two phases. In the Langevin dynamics the paramagnetic/spin glass discontinuous transition line is found to be dependent on the initial density; close to this line, on the paramagnetic side, the correlation-response plot displays interrupted aging. ; Comment: to be published on Europhysics Letters