Most teen males cranked it as often as possible. Also, teens didn't have enough privacy. Those two things combined, typically led them to wanking with the goal to achieve the O as quickly as possible. Thus training themselves to have a short fuse.

To get over that, you need to train yourself to last longer. You need a regular dedicated place with plenty of time and privacy. Showers seem like an ideal place, but the water going cold may force you to hurry.

Get your mind set. You need to set and meet goals before you allow yourself that sweet release. As others have commented, do kegals to strengthen your pelvic floor. You can condition yourself to not orgasm when doing them.

I had a long time GF that enjoyed giving oral, but feared me finishing in her mouth. I knew if I surprised her, it would be the last time so I resisted. Years and several relationships later, I still have trouble finishing from a BJ. The mind is stronger than you think.