this stage

In last some days, I have come across the discussion of marriage many times. I do not know what is happening to me and my friends but this stage surely seems marriage stage when we are about to get jobs and bored of talking of girl friends and sex. Now, probably we want to follow an organized way called marriage.
We talk about type of girl we want, her profession, number of kids we want to have(though, in totally non-serious mood), extra-marital relationship and what not. We have also started to think how we are going to spend our money and investment and stuff.
Some are still trying hard for another degree called MBA and others have decided to settle with what they are going to get from here. But I think that many of us have realized their limits at this stage and are trying to accept it in very friendly manner.
For me, I am going to be of 20 years old in few days and it is , I feel, very mature and responsible age where I can decide everything for rest of my life. I had many big dreams about myself when I was teenager. I could not figured out those dreams clearly but only feeling of doing something great, exceptional and most importantly useful to others was there. Now as I was faced by the reality in a very early and lonely stage when one side there is me and other side is whole world, I feel like a very very average person. From the little experience that I have got here, I learned that we need to have one interest or skill for which we can work for whole life. We need to get down to a very very specialized field. I am bothered by the fact that I have not got yet any such type of interest or skill.
Though, going to becoming a mechanical engineer, I know a very very little about it and could not learn much here. So I feel compelled to search for the thing I love doing. There are just too much things for me that I can never get out of them and find my true goal. It is very disappointing at the age of 20 years.