(Assuming life as we know it)<p>Early stars needed to die before there was enough atoms above helium to form rocky planets. You need to stars close enough together so that the dead stars can be formed from these remnants. There is a narrow band of stars capable of having rocky planets let alone planets in the habitable zone.  It's unlikely to form stable planetary orbits in binary star systems and stars must be small enough to last long enough to allow life to form.  etc.<p>There may be millions of planets capable of supporting life in the Milky Way, but I don't think many of them are much older than the earth.