The behaviors that you describe are certainly not the norm for a typical young adult male. The early twenties of our development tend to be the best years motivationally. Although our dedication to work and similar is not steady, the desire to be productive is. This young man sounds like he may have more than just issues of self esteem.
I strongly suspect that your grandson may be suffering from a mood related disorder. Various forms of depression exist, and the more subtle types, such as Dysthymia are very subtle, hard to identify without a clinical face to face assessment, and can even allow the person to be totally normal in some areas of functioning but depressed in others. Lack of motivation, not seeing things through and poor self esteem are common expressions of this problem.
The source of this type of issue can be both emotional and biochemical. The treatment is fortunately very well established, safe and effective. He should be encouraged to see his family doctor for a complete screening, including some direct honesty about how he is feeling and acting. And, although privacy laws prevent the doctor from sharing anything with you, that does not mean that you cannot send a note to the doctor or make a call about your concerns and observations.
Mood issues such as these are treated with Cognitive Behavioral Therapy and low doses of anti-depressant medications. The regime works, and it is shown to be effective with many different groups, but especially young adults.
The screening can also rule out other issues that can affect young males including thyroid issues, hormonal imbalances and diabetes.
I believe your grandson can be helped, but he needs to be seen for a face to face evaluation by his doctor, who will then most likely refer him for additional treatment. Although he may be reluctant to go at first, soft words break hard bones. Be encouraging, consistent and press home that this could be physical in nature. Many men would much rather deal with a physical issues than an emotional one, and they are far more likely to go if that is the focus of the encouragement. Steven