One of the things that has changed over the years is the age of my protagonists - or more accurately, the ages at which I feel certain perspectives and experiences make sense. When I wrote the first draft of my novel following Nelia, she was seventeen. Along the way, she became nineteen, and if I rewrite it again it will probably be early twenties. My protagonists have allowed themselves to be older without taking the "cheat" of being immortal - one of the pivotal characters in Butterfly's Poison is in her sixties.
I've also become more interested in families. Again citing Butterfly, one of the main hero-villains (it's a bit muddy in this particular novel as to which is which) is a widower with a daughter. Journal For The Dead, my prospective next project, follows a mother trying to find her son.
Yet I feel one of my personal goals with writing is to never forget that children and teens can be more capable, certain and wise than anyone gives them credit for. They may need more protection and they may not have as much experience, but they are not necessarily lesser creatures for their age. Kahnrey, the servant girl from Pens In Silver and Gold, ultimately provides one of the MCs with the inspiration to solve one of the central problems of the story. Civine, twelve, vivid, stubborn, tough and yet still able to see the world in simple terms, picks her father up from the shadows of the afterlife and puts him on the right path. (Ten Cities Down, short story.)
If anything, I'm a bit too fascinated with the wise child, the precocious youngster who knows more than they should ... but it isn't necessary to take that path to create a viable child-or-teen even in a work of fiction directed for a "grown-up" audience.