Actually men should be checking there 'jewels' on at least a monthly basis by the time they are 18.
The best time to perform a TSE(Testicular Self-Exam) is while bathing or showering. Hold the scrotum in the palm of the fingers of both hands and explore the contents of each half of the scrotal sac. With the index and middle fingers positioned on the underside of the testis and the thumb on top, examine the testis with a slow, gentle rolling action and feel for any small lump, slight enlargement or change in consistency.
The first time you do a TSE you can use as a baseline for future checks.
Although testicular cancer accounts for only about 14% of all cancers of the male genito-urinary system, it is the most common solid tumor found in men between the ages of 15 and 40. And it is the leading cause of cancer death in boys and in men in their 20's and 30's.