“Trying to freeze characters in particular ages/life stages is a guaranteed formula for stagnation and impactless storytelling.” Sure, but aren’t some life stages incompatible with being a superhero? If Peter Parker had preschool children, wouldn’t it be irresponsible of him to keep risking his life fighting supervillains?

What you see as incompatible, I see as potential obstacles that can be the source of good story-telling: how do you balance being a good parent and being a good superhero? Do you see superheroing as risking your life irresponsibly or trying to make the world safe for your kids to live in? How do people with an adventure-seeking personality deal with the responsibility and tedium that comes with having kids? 

(It’s almost like a metaphor for career vs. family struggles…)

And one of the ways that I know that it can be a source of good storytelling is that it’s been done before: the Fantastic Four have kids, X-Men have had kids, Luke Cage and Jessica Jones have kids, Jessica Drew fought a Skrull invasion immediately after giving birth. 

So no, I don’t think there are life stages incompatible with being a superhero.