Greetings there, Thanks for your question. I am Dr Asanghanwa Carlson. I acknowledge the fact that premature ejaculation is a serious problem which can be very disturbing in a couple as it brings down self esteem especially for the male counterpart. Premature ejaculation is rapid expulsion of semen from the penis with minimal stimulation. How rapid? is the major question however this can be less than two minutes in most cases. The fact that you mention your penis is small, soft and weak leads me to think you have a psychological component to your problem such as in performance anxiety. This can be a major cause of premature ejaculation, the fact that you are anxious about your performance with your partner. The fact that you have masturbated for over 16 years is no issue in my opinion. I think you should talk out with your partner, see a sex therapist if it persists. Also, other underlying conditions such as diabetes and antipsychotic medications might favour premature ejaculation. This however is to be verified. I would simply advice you to talk with your partner, see a sex therapist. Have a great time and good luck