Final answer:
The middle-aged man's diagnosis would best fit in the category of impulse-control disorders according to the DSM-5.
Step-by-step explanation:
The diagnosis for the middle-aged man who cannot stop gambling would best fit in the category of D. Impulse-control disorders according to the Diagnostic and Statistical Manual of Mental Disorders 5 (DSM 5).
Impulse-control disorders are characterized by the inability to resist urges or impulses that may be harmful to oneself or others. Gambling disorder is specifically classified as an impulse-control disorder in the DSM-5.
In order to be diagnosed with gambling disorder, the individual must exhibit symptoms such as persistent and recurrent problematic gambling behavior, experiencing distress or impaired functioning as a result of gambling, and exhibiting an increasing need to gamble with larger amounts of money to achieve the desired excitement.