According to the search results, the normal size of the prostate at the age of 70 can vary. However, the normal prostate size is about 20 to 25 grams in men between the ages of 21 and 30, and this weight remains essentially constant with increasing age unless benign prostatic hyperplasia develops. Only 4% of the prostates in men more than 70 years old reach sizes greater than 100 grams. Another source states that the normal prostate size is 4cm wide, 3cm long, and 2cm anterior and posterior diameter. It is important to note that prostate size can vary from person to person and can be affected by conditions such as benign prostatic hyperplasia. Therefore, it is recommended to consult a healthcare professional for personalized information regarding prostate health.