First of all, if someone tells you that you can last as long as a porno actor they are misleading you - the adult movies are not real, like any other movie, it is acting.  They simply shoot the movie over days or weeks and then edit it to appear as if they male actor simply does not ejaculate.

So do you think you have a problem?

Actually most people who think that they have a problem actually don't.  The best way to measure is it to look at the clock when you first start to become hard.  And then have normal sex and check the time when you actually came.  Of course there are times when you want a quickie but for a very typical lovemaking session, this time should be 20-30 minutes.  You can extend this time by having more foreplay or asking your partner to slow down but if you ejaculate as soon as you are inside her or after a minute or less or outside (that is the worst), you have a problem.

Now don't get depressed or think that your case is hopeless or that something is terribly wrong with you.  We all need to learn sex like we learn anything else in life.  Dr. Paolo Amino has a great guide on stopping premature ejaculation on your own using simple techniques.