First two beta readers are 11 years old.

While waiting for them to finish: I found a problem with my writing.  It's hard to believe that I keep finding errors at this late date. (Or is it?)  This revelation comes from reading other similar stories and gaining experience.

The Problem:  I was way too heavy with compound and complex sentences.  Hence:   The word "And" shows up on every page like splattered ink.  I went through the story and either replaced or restructered about 80% of the compound sentenses and many of the complex ones.  It reads much better now.  See tip #9 in "Tips" link.

The Lesson: Grow your skills by comparing to similar published works, look at everything in your manuscript, then rewrite, rewrite, rewrite.  Don't rush to a premature finish.