EDIT: Figured it out, the limitation was between the chair and the keyboard 
Just needed to give it a uv map to store the age data in, then can use that to drive a ramp. Now to figure out if I can store velocity too. Can’t wait for transferable by distance houdini style attributes in everything nodes!
Trying to get the particle info node to control the colour of the result from an explode modifier, but it doesn’t seem to want to play ball.
If I’m not missing something stupid, is this likely to be classed as a bug or just a limitation?