What are the ages of the characters in Oliver Optic's Rich and Humble?

Though not every character in Oliver Optic's Rich and Humble has an age given, certain characters -- including the titular Bertha -- do. Bertha is 13 years old during the events of the book.
Bertha reveals her age when she applies for a job with Mrs. Byron, explaining "I am nearly fourteen." Mrs. Byron is incredulous at her age because Bertha claimed to have experience teaching children. Bertha explains that she does -- experience teaching at a mission school and that it was volunteer work and not a job. 
Mrs. Byron attempts to use Bertha's age against her when they negotiate salary, saying, "You are rather young, especially for the salary you ask." But Bertha insists on her three dollars a week and prevails. 
The boy who Bertha cares for is Charley Bryan, who is described as "about six years old."
A boy from near Bertha's home of Woodville, Griffy Von Grunt is described as "a stout, fat little Dutchman, of ten years of age."
Bertha's brother Richard is fifteen years old.