No, don't worry. 12 year old boys often are entering puberty and it is a time of privacy and discovery. It's private and healthy--unless he uses all the hot water! If his behavior worries you, speak to him about it and mention that you noticed he is taking longer. He might shorten his time. If you feel that something is uncomfortable then ask his pediatrician to talk to him in private.
Wayne Yankus, MD, FAAP
expert panelist: pediatrics