Hello, this is Dr K.. Answers are not medical advice and do not constitute a doctor/patient relationship. I look forward to helping you today.
Your libido does decrease as you get older which is due to a combination of factors- decrease in testosterone that occurs in some men but not all, excess weight, concurrent medical problems, relationship issues, and circulation to name a few.
Prozac will decrease your desire and performance.
Your penis will be small if you are overweight, its hidden in the fat pad in the pubic area
If you do not want to take medication, consider exercise and weight loss and a trial of a different antidepressant like Wellbutrin.
Hope this helps