Smoke Particle Emitter - Density based on Particle Age


I’m setting up a smoke sim using a particle system to emit the smoke. The density of my particle smoke flow is set to 1, but I don’t want it to be 1 at birth. Instead, I like for the density to gradually build up as the particle age over 12 frames. so at particle age 1, the smoke density emission should be 0 and at particle age 12 the density emission should be at 1. Is there a way to based the smoke flow density based of particle age? Thanks in advance.