We understand that this situation is upsetting for you, but people who care about you obviously feel that there is some cause for concern. Four years is a big difference at your age. Research has shown that girls who date older men tend to have sex before they want to, have higher pregnancy rates and higher rates of contracting STDs. While this may not be the case for you, your parents are clearly concerned that there is a power imbalance between you and your boyfriend and that it will be difficult for you to make healthy sexual decisions with someone significantly older than you. Furthermore, in most states, it is illegal to have sex with anyone under the age of 14, or for people more than four years apart to have sex when one partner is under 18 - another cause for concern.
We suggest you have an honest conversation with your mother. Tell her how you have been feeling, and try to see her side of the story - she clearly cares about you. If you cannot speak with her, we think it would be a good idea to confide in someone about this relationship - another older relative, or a teacher or counselor at your school.
If your boyfriend cares about you as much as you care about him, he will respect you and your decisions about sex, and be willing to talk openly and honestly about it. Thirteen is very young to be having sex. While the decision to have sex is ultimately yours, it is important that you take into account that having sex can put you at risk for sexually transmitted diseases and pregnancy, not to mention that you may not be mature enough to handle the emotional impact of a sexual relationship. We recommend that you do not make the decision to have sex without talking it over with an adult who you trust. And if you do choose to have sex with him, we hope you will do it safely.