It is happen to whole Japan!!!
Or in several countries humanities courses are trying to decipher the "Marriage Strike", and so on.
The thing is, there are several problems that make having a family hard, and even when you don't want a family, and want just random sex, some problems still get in the way.
Personal anecdote, but good example: I am 29 right now. Also right now my interest in having a girlfriend dropped through the bottom, I am less interest now than any point in my life (even in my childhood I was more interested).
After some self-analysis I concluded the reason is very simple and obvious: What I would want a girlfriend for? I don't have any money (literally), I still have lots of debts (made to pay student debts), I don't own a house, or a car, or even a bicycle, I spend most of my time trying to sharp my work skills in hopes I can finally get some decent money having my first job (yep, I graduated in 2009, and never had a job!) or by getting some decent contract (I had many contracts, but mostly crappy ones that I took only because I had no other choice, since I am in debt).
If I had a girlfriend, she would "get in the way", it would make my life worse, not better, I don't have time even to buy my own food, what would be the point in having someone to share things (including time) with?
And I believe this applies to most of my friends and acquaintances too, even the ones in other countries, life is just too fucked up right now to people between 20 and 35...
In UK humanities courses even invented a new name for my generation: "Boomerang Generation", the only generation where large numbers are being forced to live with their parents unwillingly, even after attempts to leave home, the generation that in hopes of being proper adults rented some place out, failed to pay, and were forced to return to their parents home, like a boomerang.