vale berry
I think it’d help if you would just show us some of your sketches that run into the issue you’re facing. From what I gathered you’ve said you’re trying to soften up the heads you’ve drawn but they end up making the character look younger than they are.
To retain the likeness of the subject you’re drawing when it comes to stylized is mainly their features that set them apart from a joe. I’m pretty sure this is what caricature artists do— and you should probably look into some of them. Proko has a whole section of it.
If the artist you’ve posted is what you’re aiming for then I don’t think you need to “soften up” the heads that you draw. The artist’s stylization looks to be found in their rendering. But they too an extent have accurate anatomical proportions (except for the nose oc)
If head construction is a problem for you— find methods of which people construct heads such as Loomis method, Bridgman, Reilly etc
Id just strongly suggest posting something you’ve worked on.