Young foreskinned males who have escaped circumcision in infancy face new risks of circumcision as they enter puberty because the foreskin is still developing and may not be immediately retractable. Circumcision is a nice word for the very harmful surgical amputation of the foreskin part of your penis and the permanent irreversible loss of its functions, which results in lifetime disability and handicap.

These young males are likely to be preyed upon by unscrupulous physicians who see an opportunity to earn a nice surgical fee for performing a circumcision. Young teens have reached an age where they can refuse harmful unwanted surgery and should do so when offered an irreversible adult style circumcision.

The British website, 4-skin Health, offers advice for teenagers and young adults.

Young males whose foreskin is still tight and difficult or impossible to retract may engage in manual stretching daily over a period of time, during which the daily stretching will cause the narrow part of the foreskin to stretch and become retractable. WikiHow gives full information on how to pull one's foreskin back without pain.

The daily or twice-daily stretching works by causing tissue expansion through mitosis. 

One should not force retraction and one should not cause oneself pain.