noob re data channels and resetting particle age

[naxxar]

Sorry for what must seem a dumb question. I have reduced this to a very simple sim. So, I have a stream of particles (even just 1) falling as Physx shapes and colliding with a plane. I send out to next event and want to reset particle age to zero. Custom properties is not doing it because I still havent worked out how all  the data channels , custom floats etc all work. Is there a simple tut that you can point out to me?
Many thanks