There are so many reasons why you're having problem on having a hard penis. Some men have the same problems like yours. These problems occurs at any age but they are most common in older men. First you need to know what might be the causes. Here are some causes you might want to consider:
1. Health problems such as high blood, diabetes, depression etc.
2. Stress
3. Being alcoholic and smoking
4. Past surgery or medical history
5. Physical problems
6. Psychological matters
7. Lifestyle changes
8. Medicines you are currently taking
9. Not having exercise at all
10. Sexual expectation