The Niagara content examples project has a emitter called DynamicBeam_Emitter. I go in and add a Color module with Lerp Linear Colors. For LerpFactor I set the following expression: frac(Emitter.Age). The color never changes, the LerpFactor and therefore the Emitter.Age remains 0.
However if I do the exact same thing in the StaticBeam template (offered when creating a new emitter) then it works as expected. I went through and compared all the settings but couldn’t find the reason of the unchanging Emitter.Age.
(Btw Particles.Age also seems to be 0 in the former case.)
Niagara is very raw system on it core and lot of attributes need module that will process and update them, and Age is not exception. It build this way to be elastic system which you can modify even smallest aspects of particle system.
There module called “Emitter Life Cycle” for emitter and “Update Age” for particles and you need to place them in Update pipe of both top make age attribute work on both. If they missing age will always be 0. They might be missing age is not needed.
If for some odd reason they don’t work, recreating age is super easy just add DeltaTime (time between frames) to Age attribute and and you got updating Age, that what modules mentioned above actually do too