How can I draw the form (or indicate) the brow ridge in this front facing skull drawing?

What are some things I should incorporate in my skull study? Currently, I’m only drawing the skull over and over to see the underlying form, but I believe I missing out on something important.

I’m not certain how I can create more detail in the eyes without shading. Why would you suggest?

I drew these characters’ heads with an age range in mind. Tell me what you believe their ages are, and what I could do to construct a more accurate depiction of the age range I aimed for. Age range for boy: 10-15 Age Range for girl: Early 20s Thank you. .

Good Day. I started the Simple Structure Project of drawing a pear, but I got this far and I honestly don’t know HOW TO finish. Any suggestions?

Good Day. Any advice for my drawing of the pelvis? These all came from my imagination. (Except 1)