Conservative Treatments -- Norm-UK
The foreskin and the glans develop as one structure. Natural separation of the two structures occurs gradually during childhood. The age at which the foreskin becomes retractable differs for each child. It may take until the age of 17 or beyond. This is normal. Forcing the foreskin to retract may cause pain, bleeding, scarring, infection, and adhesions. Therefore, the foreskin of a child should be retracted only by the child himself when he is ready to do so.
http://www.norm-uk.co.uk/contreat.htm.