You are blessed with a protective, highly-innervated, erogenous full-length foreskin. Many unforeskinned guys would envy your foreskin. You display great wisdom in wanting to avoid circumcision.
You should thank your parents for protecting your physical integrity. Because of your physical integrity you will be able to have sex the way nature intended it.
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. You are normal for your age. These foreskins may be gently stretched over a period of time to cause them to widen.
It is not necessary to have a foreskin that will retract. Some 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 non-retractile foreskin has more sensation and that sex is better. However, there is no scientific evidence one-way or the other.
To retract the foreskin, one must grab the foreskin on the shaft and pull it rearward. If the foreskin will not retract then you must consider leaving it as it is or doing stretching exercises. It depends on just how tight your foreskin is. If it is really narrow 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 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. Do NOT cause yourself pain. 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. Search the Internet for: Willy Well-being and you will find the information you need.
Is it tight or is your frenulum too short? If it's just tight you can stretch it by pulling it back in the shower or bath when you have an erection. Just hold it back as far as you can without hurting yourself for a few minutes every time. Or if you can get two fingers in the opening you can stretch it that way.
If it's the frenulum that's too short you will probably have to have a doctor cut it.