Evans, you may be suffering from erectile dysfunction. At your age, it is not likely that the problem was caused by an underlying sickness. It may be that you were too anxious or emotionally stress. Try to calm yourself when having sex. Practise foreplay more before you penetrate. I would advice against using sex enhancement drugs at your age. They side effects may greater when you are around 40. If possible take warm water before sex and practice foreplay more. You can also abstain from sex until you are married.