These powers received due admiration from Catherine, to whom they were entirely new, and the respect which they naturally inspired might have been too great for familiarity, had not the easy gaiety of Miss Thorpe's manners [...] softened down every feeling of awe, and left nothing but tender affection. (4.9)
Catherine's feelings of awe towards the older and seemingly wiser Isabella are significant here, as they point to Catherine's tendency towards hero worship.
Perhaps Catherine was wrong in not demanding the cause of that gentle emotion - but she was not experienced enough in the finesse of love, or the duties of friendship, to know when delicate raillery was properly called for, or when a confidence should be forced. (5.2)
Catherine's lack of experience in relationships, as well as her emotional immaturity, creates uncertain situations for her. Words like "duties" and "to know," suggest the ways in which relationships are conducted by certain rules that the young and inexperienced Catherine will need to learn.
[B]ut, where youth and diffidence are united, it requires uncommon steadiness of reason to resist the attraction of being called the most charming girl in the world. (7.44)
Catherine's youth helps to make her gullible, or easily trusting. She is at least partially swayed by John's compliments, even as she finds him increasingly annoying.
Her manners shewed good sense and good breeding; they were neither shy, nor affectedly open, and she seemed capable of being young, attractive, and at a ball without wanting to fix the attention of every man near her, and without exaggerated feelings of ecstatic delight or inconceivable vexation on every little trifling occurrence. (8.11)
Eleanor becomes a good example of how to be young without being obnoxious here. The diction, or the words used to describe Eleanor, also places Eleanor in direct contrast to Isabella,
Catherine did not think the portrait a very inviting one, but it was too late to retreat, and she was too young to own herself frightened. (9.10)
It seems that Catherine suffers from some youthful pride here, though her youth could again be combining with her shyness to prevent her from speaking up after John scares her with his description of his crazy horse.
Away walked Catherine in great agitation, as fast as the crowd would permit her, fearful of being pursued, yet determined to persevere. As she walked, she reflected on what had passed. I was painful to her to disappoint and displease them, particularly to displease her brother; but she could not repent her resistance. (13.24)
Catherine shows strides towards growing up, as she stands up to the peer pressure of the Thorpes and her brother. Though Catherine is still worried about displeasing others, she doesn't cave to pressure.
"Young people will be young people, as your good mother says herself. You know I wanted you, when we first came, not to buy that sprigged muslin, but you would. Young people do not like to be always thwarted."
"But this was something of real consequence; and I do not think you would have found me hard to persuade." (13.35-6)
Mrs. Allen's philosophy on young people is problematic here. She lets Catherine do what she wants, thinking that "young people" like to have their way. But Catherine shows a lot of maturity by noting that she would appreciate some guidance in a strange new place.
"All those things should be allowed for in youth and high spirits. What one means one day, you know, one may not mean the next. Circumstances change, opinions alter." (18.18)
Isabella links youth with freedom of behavior here and seems to think that rapidly changing opinions is a prerogative, or privilege, of youth. Isabella seems to suggest that youth shouldn't be held accountable for changing their minds. This makes sense, given Isabella's irresponsible behavior – she doesn't want to face consequences.