Thank you for your question.
Premature ejaculation is a very common complaint. Usually all boys start with ejaculating quickly. They learn through masturbation and experiencing sex how to delay ejaculation and prolong the erection. Generally boys who have freedom to experience their emerging sexuality, ask questions and have access to good quality information about sex and masturbation have much better experience with delaying ejaculation. If sex or masturbation is associated with guilt, anxiety, nervousness or fear boys learn to ejaculate quickly in order to 'get it over with quickly'. This sets the stage for developing premature ejaculation as a dysfunction that adversely affects their ability to enjoy and manage their arousal and hence satisfy their partner which then creates more anxiety.
The good news is you can learn to delay ejaculation by practicing correctly using some well prescribed masturbatory exercises. You may wish to read 'New male sexuality' by Bernie Zilbergeld and ' Managing premature ejaculation' by Metz and McCarthy.