It depends on just how tight your foreskin is. If it is really tight and absolutely won't retract, then you can have penetrative sex without pain. On the other hand, if it just a little bit tight, then it is likely to be forced back during sex and that will hurt because it is tight.
It is not absolutely necessary to have a foreskin that will retract. A few men live their entire lives with a non-retractable foreskin. They can masturbate, have penetrative sex, get married, and father children with a foreskin that does not retract. Some believe that a penis with a tight foreskin is more sensitive and that sex is better. However, most men prefer to make their foreskin retractable.
Almost all boys are born with a foreskin that does not retract. This is normal. It takes years for the ability to retract to develop. About ½ of boys have a retractable foreskin by 10.4 years of age. Many adolescents still have foreskins that have tips that are too narrow to pass back over the penis head. These foreskins may be gently stretched over a period of time to cause them to widen.
It is normal for teens to have a foreskin that does not retract. One’s foreskin is still developing. One can help it develop by stretching it.
When your penis is erect, gently pull your foreskin back against the head of the penis. As the head attempts to pass through the foreskin it will stretch the skin a little. Do this every day and in a few weeks or months your foreskin will widen and you will be able to retract your foreskin. Do NOT force retraction.
It works by tissue expansion. Stretching skin induces “mitosis” which is a word that means “division of cells”. New skin cells are formed and the skin expands but it takes some time. The increase in size is permanent. Be patient and give mitosis time to work.
The important thing is to put the skin under tension every day so that it will grow wider.