This step is really only important if you plan to rig + animate your portrait. If that’s not your plan, then this concept and video can be ignored.
But in the case of rigging + animation, even young faces have high potential for wrinkles when deformed (even when no wrinkles are present in a neutral state). Chris Jone’s incredible example showcases this:
So for highest fidelity facial deformation, it’s wise to consider key wrinkles being compensated for in the retopologized base mesh. Here’s another example showing a [young] character in Avatar and how wrinkles potential is built into the base mesh:
