What’s up, TDRD?
I know that scaling can be a pain in the arse, and there are many ways one can go to get the same results. The direction I prefer to go, however, is taking a Genesis figure, and if I’m aiming to decrease the age, is add the “Basic Child” shape in Genesis (found in the Parameters -> Actor -> Universal tab). It works a lot better than the K4 scaling route in my opinion.
In the first image, I took the default Genesis figure, and applied the “Basic Child” morph at a dial setting of .25. I also changed the color of the morph tab so it is easier to locate on the image for this example (figure 01). If applied at a dial setting of 1.0 it results in Genesis being shaped like a K4 figure.
This may not be all the work you have to do. Naturally, you may have to increase the scale of the head. You can find this under Shaping -> Head -> Proportions and it is labeled as “Propagating Scale”, which I set to 3.0% (figure 02)
Of course, you may have to make modifications based on the look you are going for, but you can change the Genesis figure’s UV set to accept your K4 textures, or for the Genesis male or female textures.
I also want to take a moment to point you to a fantastic tool at Share-CG (a free Poser and DAZ repository) that can be pretty durn helpful.
http://www.sharecg.com/v/41322/View/11/Poser/Poser-dial-driven-measuring-tools
It is a scaling tool that uses M4 as it’s base (and considers that M4 is measured at 6’0”) and is a great way to get some sizing between characters.
I hope this information help, good luck!

Click thumbnail to see full-size image