Yikes, akon, someone gave you some really awful information.
Masturbation is extremely healthy. As Anne mentioned, frequent masturbation can even lower a man's chances of getting prostate cancer later in life!
There are no bad side effects to masturbation assuming a person does not:
1. Masturbate with sharp objects
2. Masturbate so much that it interferes with the rest of their life
That's easy for most people to avoid, right?
Most men masturbate. Some of them last long during sex, some don't. Either way, it's not a result of masturbation. Sex and masturbation are two different things. If a person lasts for, let's say, two minutes during masturbation, that does not necessarily mean they will last two minutes during sex. I can orgasm in about 30 seconds during masturbation, but I need about five to ten minutes to orgasm during sex. That's because the two things, although somewhat similar, feel rather different.