My wife is quite insightful for a low functioning dBPD. She admitted that she feels like she has the emotional maturity of a toddler and said she feels that's why she is so defensive of our toddler's testing behaviors. In fact in her words she believes that he should not be disciplined or given consequences for his behavior, but given a chance to be acknowledged empathetically and guided morally into wanting to improve his behavior. I think that is amazingly insightful thinking, however, it does not work so well with a pre-speech two year old... . 4 does sound about right.
Problems arise as the child grows and becomes aware that in many regards they are more mature in certain aspects than one of their parents. They suddenly loose respect for the parent and the parent with BPD sees them as a threat, this leads to serious domestic conflict.
It's so hard to describe all the feelings I had as a child when I realised this about my mom. Pity, anger, contempt, and a feeling of having been cheated in having her as a mom... . those were the four strongest ones. It became
impossible to respect her, frankly... . I was nine when the maturity gap had become so wide between she and I that I began to see her as a screeching, out-of-control toddler in an adult body.