Schnitker and Emmons (2007) found evidence for an inverse relationship between patience and negative affect and between patience and depression, but a positive relationship between patience and self-reports of certain negative health outcomes, including headaches, acne, and ulcers.
They found that trait stability increased from a correlation .31 in childhood to .54 during the college years, to .64 at age 30, and then it reached a plateau around .74 between the from age 50 until the age of 70. What we can infer from these results is that personality seems to stabilize with increasing age.
To be diagnosed as a personality disorder, a behavioral pattern must cause significant distress or impairment in personal, social, and/or occupational situations. These disorders typically aren't diagnosed until an individual is a young adult, often not until their 20's or even 30's.