Driver from particle age?

Is there a way to drive a value, Scale maybe, with particle age?

Yes,

You can use a texture applied to a particles system (not object) to drive various particle features, Size being one of them. In the attached BLEND file the color of the RAMP represents age over time. When white, the particle will be the size specified in the Particle Settings. When black or grey, it shrinks in size.

Attachments

266_particle_size_by_age.blend (205 KB)

Thanks, your a lifesaver – I totally forgot that the texture datablock for particle systems even existed! Thats exactly what i needed.
Basically, I have a matrix style bullet trail emitting surfaces that i can use to distort the backround in the compositor for that speed warp effect but needed them to slowly scale up as they aged, perfect!