Hello, This is a usual teenage problem. When you start mastrubating often then the time needed for ejaculation decreases. Most part of this premature ejaculation is psychogenic. In order to gain back control over your ejaculations I will advise you few non medical therapies. First avoid mastrubating too often. Max twice a week. When you mastrubate, foreplay as well as you can try holding the ejaculation voluntarily before it starts to flow. Interuppt it twice or thrice and then feel and ejaculate. This way you can progressively enhance the time you need to ejaculate. If you still find it difficult after a month or so consult a urologist for medical therapy.