It is normal for infants' and childrens' foreskins to not be able to be retracted. Some boys maybe be able to retract their foreskin as early as age 3, while for other boys the foreskin will not be able to be retracted until puberty.
When the foreskin can't be retracted in adult men it's known as phimosis. This condition can be treated by a series of stretching exercises and a topical corticosteroid cream over a few weeks or months. This option is popular with many men as they are able to keep the foreskin and avoid a painful circumcision. You should consult a urologist for help treating this problem.