One thing I always find tricky is drawing people at different ages. So I've collected a few resources here - selected pages from books about the subject - and let me know if you are aware of any other good ones I've missed.
Also in a future post I will jot down a few I have observed myself over the years and that I find helpful.
WARNING - there are drawings of naked people (at different ages) below! If you are offended by such things, you've been warned...
This one is from The Famous Artists Course and it's a good breakdown of how the head changes at different ages.
This page is from Andrew Loomis's "Figure Drawing For All It's Worth".
And here's another page from Loomis's book where he talks specifically about baby heads.
These are from "Atlas of Human Anatomy for the Artist" by Stephen Rogers Peck.
Both Loomis and Peck make the point that the "center line" (where the midpoint of our bodies lies) changes as we grow older. Loomis represents it in his drawing with a cross at the midpoint; in Peck's drawings it is represented by a dotted line.
Here's one by Peck that's a map to where wrinkles form.