Is first contact always pleasant?

Judging from poll – for 30% it hasn’t been so. The most common cause for it – failures in sex (problems with ejaculation or erection), unpleasant feelings, or man just doesn’t reach the expected enjoyment. It has different causes. Firstly it’s stress and worries about what and how it will be. Am I a real man? Is it going to be fine? Will I know what to do? Secondly disappointment might be brought by very process when something is not going the way it was planned. For instance – everything is going its way and suddenly erection disappears or ejaculation happens too fast. Thirdly, if during sex we don’t get the pleasure we expected, we have a feeling of emptiness after intercourse. Those reasons are many and can vary a lot for each person.

What are the biggest problems during first sexual intercourse?
What age does first sexual experiences usually happen?