Hello, my young friend: First of all, I would like to thank you for bringing up this question to my attention! Your mouth/ tongue feel bitter after you swallow the sperm of a thirty years old man. There are quite a number of reason why your tongue turns to bitterness. Semen made up many different chemical compounds in it. Number one reason it taste bitter is that old friend's personal hygiene issue. If he didn't keep a good body hygiene in his private area, allowing sweat to stay around that area, it will affect the taste of his semen. Other important contributing factors includes, but not limited to, consumption of alcohol, smoking, use of drugs, certain kind of food, such as Asparagus, onion, garlic. If you tongue taste bitterness after that particular encounter event, then, if you want to get rid of the bitterness on your tongue, you may try to use several of the following remedies. (i) try to use about 0.5 - 1.0 oz of Vinagar to rinse you mouth a couple times a day for few days. Or (ii) use an over-the-counter mouth wash such as Listerine to rinse your mouth twice daily. (iii) brush you tongue after you brush your teeth. (iv) chew/ eat a few small wedges of fresh lemon, allowing the lemon pulp stay in your mouth, for just about a minute and swallow the lemon pulp. The best way to not to have the bitterness on you tongue is that I would strongly suggest you NOT try to swallow anyone else's semen from now on. If ,and only if, you want to do it again, then just swallow your own semen. Why? It is because semen from other people, like blood, can carry many blood-borne pathogen such as Sexually Transmitted Disease, including, but not limited to AIDS, Hepatitis, which is in-curable in today's medical technology. Your own blood and your own semen are " relatively safe and clean. The should be no foreign germs under normal circumstance. In fact, it will be even better that you should not be engage in oral sex with anyone else. Bacteria and viruses ( for example herpes ) can also be transmit from other people into your mouth during oral sex. God has given you a male body. Your body is still growing physically, mentally and emotionally. I would highly encourage you to learn to develop a normal and healthy social relationship with opposite sex. There many good sources you can learn how to develop a healthy relationship with female friends. If possible, I would really encourage you not to continue having the abnormal sexual behavior with another old boy/ man of the same sex. You can ask for help in school counselor, a medical doctors, or a clinical phycologist. I hope that this will help you and give you some positive advise ! Blessings to you !