How are infancy, childhood, adolescence, and adulthood defined? How would you diagnose Leo's experiences? Leo often feels sad and tends to be very sensitive to criticism. When he was younger, Leo used to enjoy watching sports and going to sporting events, but he now feels that there is no point to these things. He has never experienced suicidal ideation, does not tend to be excessively guilty, and has had a stable weight for several years. About three days a week, Leo becomes very energized and will do things like stay up all night reorganizing the kitchen, garage, or living room. If someone calls Leo when he is in an energized mood he talks very quickly and excitedly but is not rude. Around once a month, he makes a large purchase online or engages in some medium stakes online poker. He is still able to pay his mortgage and put food on the table. Leo still shows up to work generally doing a good job. He dates occasionally and has some friends through work. Leo appreciates when people give him space when he wants it. Leo says, "I have a good job and I'm doing fine. Nothing is wrong." If you were Leo's treatment provider, what would you diagnose Leo with and why?

Here are the definitions:
Infancy is usually the period of childhood before a baby learns to walk.
Childhood is the time period from a person's birth to the beginning of adolescence, which begins with puberty.
Adolescence refers to the time period after the beginning of puberty until a person reaches adulthood.
Adulthood is the period after someone is fully grown and developed.
Leo is likely suffering from bipolar disorder, also known as manic-depression (see the link below for more information). People with this mental illness suffer from periods of depression intermixed with manic periods during which they often experience changes in their sleep patterns and energy levels. Leo is clearly suffering from mild to moderate depression, as he has lost interest in activities he used to enjoy, though he does not have other serious symptoms of depression such as gaining or losing weight or being suicidal. He experiences periods of intense activity in which he stays up all night and then he speaks very quickly, which can be signs of mania. He also occasionally spends a lot of money, which is also a sign of mania. However, none of these symptoms are severe enough to interfere with his work. Therefore, he likely has a mild to moderate case of bipolar disorder. 
https://www.nimh.nih.gov/health/topics/bipolar-disorder/index.shtml