Question: my age is 25 ...and my penis size is 4.5 inches". Is it normal healthy size..or i have some problem,due to which it is not large? Is is enough for reproduction?

Your penis size is a little below "normal".   The average size of the penis in the United States is about 6 inches.  A penis this size is not considered a medical condition, just a little on the smaller size.  There are ways to gain extra length if the size concerns you.  Using an extender device, such as the one available from Fastsize, will give you between 1-3 inches, making you an average size.