Sure

Assuming you were able to create your basic path curve, and attach your PFX brush to it, in order to make it look like it is being "drawn" or animated from one end to the other:

1. Select your brush on the Outliner or hypergraph.
(whichever you use. I use the outliner because I'm more comfortable with it)

2. Now, to see the attributes of any selected object, there are 2 methods you can use: the "channel box" or the "Attribute Editor".

-The Channel Box appears in the Maya window only if you choose to display it. It appears to the right of the workspace.
NOTE: You can display either the Channel Box or the Attribute Editor in the main Maya window, but not both at the same time.
If it is not there, go to:
Display > UI Elements > Channel Box/Layer Editor

-To display the Attribute editor window, simply select your object and on your keyboard, hit: CTRL+A

3. Once you have accessed the attributes of your selected brush, look for the MIN and MAX CLIP attributes.

4. Now you can key these attributes just like any other object.

- Render a test frame to see what the full brush looks like, then:

- change one of the clip values, then render another frame to see how these new attribute values make the brush stroke look as if it is getting shorter, or longer. (depending on which attribute you chose to play with)
One value controls clip from one end, while the other value controls clip from the other end

- to key an attribute, simply place your mouse pointer over the value box, then right-click and choose KEY SELECTED.

- then go to another frame in your frame range, and change the value(s) to whatever you need, and key it again.

- rewind the timeline and watch as the brush stroke gets longer or shorter over time, depending on how you messed with the values

Good luck!