I am 28 years old and i sometimes feel that my penis is not that much hard as it used to be.. why and what should i do?

"Hard" to remember: It's very difficult to remember what you did last week, much less what your penis was like years ago. Make sure you're avoiding alcohol, tobacco and weight gain. Certain medication can also cause problems. There are various physical and psychological causes for erectile changes, commonly including stress, anxiety and increasing age. If really worried, ask your doctor.