Newfoundland Teenage Years?

[TheGreatestManEver]

Im trying to convince my parents to get a newfoundland but shes worried about are cavalier king charles spaniel because he doesn't have a great back, I think he will be able to handle himself hes been around a rottweiler, grew up with a golden retriever, I think he just needs to that he makes the rules, I just want to know what the newfoundland teenage years are like.