there is no formal diagnosis or recognized mental health disorder called "immature personality disorder" in the official diagnostic manuals such as the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) or the International Classification of Diseases (ICD-10).
It's important to note that personality disorders are complex conditions that involve enduring patterns of behavior, thoughts, and emotions that significantly deviate from cultural norms and cause distress or impairment in various areas of an individual's life. There are several recognized personality disorders in the DSM-5, including borderline personality disorder, narcissistic personality disorder, avoidant personality disorder, and others.
It is possible that the term "immature personality disorder" might be used informally or colloquially to describe certain traits or behaviors related to emotional or cognitive immaturity, but it is not a formal clinical diagnosis.
If you are concerned about your mental health or someone else's mental health and suspect the presence of personality issues, it is essential to seek professional help from a licensed mental health practitioner. A qualified mental health professional can conduct a comprehensive assessment, provide an accurate diagnosis (if applicable), and develop an appropriate treatment plan based on an individual's specific symptoms and needs.