Too Serious, Too Soon?

Everyone knows that at the beginning of a relationship you tend to have that 'honeymoon period'
where everything is perfect, and you don't know what could possibly go wrong in your relationship
etc etc.

But there are those couples who don't seem to ever leave that stage. The couples who think they'll
be together forever and nothings going to break them up...
Well i'm not saying there's nothing wrong with that, always good to have a little optimism in
your relationship right?

And there are those couples who move in together after say, what? 3 weeks? a stupidly little amount
of time, get engaged after only a couple of weeks and are married in the space of a month?

Each to their own and all that, but when is it acceptable to start making those more serious
decisions and steps into your relationship?

You hear the lovely fairtale stories where a couple will meet, know they're meant to be together
and make those decisions and take those steps in a short amount of time and are still together 50 years
later and all that. Which is sweet as hell, don't get me wrong. But the reality is, many people
are so so wrong when making those decisions so early.

I'm only 19 years old, and i've watched alot of my class mates settle down with their boyfriends
more or less as soon as we finished school at 16, and had kids. All of their relationships fell
apart within the first few months of their babies being born (at the most).
Is this all part of the adolesent obsession to grow up and be adults?
My friends at uni, who are in new relationships talk about how they're talking with their partners
about moving in together when they've finished uni. Which after the 2 years we still have of Uni
is a little more sensible, but their relationship was still in the first couple of months stage.
Are people now a days that desperate to settle down and have their life sorted?

Not that I want to dampen anyone's happiness or anything. I just don't see the rush in getting so settled down so quickly.

I know a girl who was in my younger brothers year at school, by the end of school she had 2 kids. I agree that kids are some of the most amazing things to have in your life, but at an age so young, what else are going to know other than your kids.
I believe people should have other goals in their life, rather than find a boyfriend, settle down and have kids. Even if it is just to go out and enjoy the younger years you have, you won't be able to do so much of it by the time your kids have grown up and you have that freedom again.

What are your views on how long you would personally want to wait till making the decision on
moving in with your partner, marriage, etc.