You've all seen this in anime and manga, right?
I've seen it a lot over the years.
It usually comes from someone older, saying something like "it must be nice being young", or "the wonders of youth" or something to that effect.
It is especially frequent in Bakuman, the last manga I finished, where I can think of at least seven cases at the top of my head.

So now I'm curious. What IS this obsession that Japan seem to have with youth?

Well, it's more cultural than anything.

Only in Japan will you see the (somewhat sad) sight of 30-or-so years old women talking with a high pitched voice and dressing up like adolescent girls. Only in Japan will you see that panty vending machines are a socially acceptable way for old men to relive their youth by sniffing young girls' (dirty*) panties.

* Yes, they really have vending machines with dirty panties in them. Look it up.

Well That Vending Machine Bothers Me JUST A TAD.

I thought dirty panties vending machines was common knowledge.
Anyway, that's really only an elaboration on the subject.
I want to know what exactly it is, and WHY they have this obsession.

As I said, it's part of Japanese culture. You'd have to go back to the days of the samurai to understand what's up there. But it's really the way how girls are treated in the community and how the desire to become young has cultivated over the years within that community. A young person stands for a creative, energetic and beautiful individual. Once you become old, you become ugly, you lose strength and you run out of ideas. That's how it is in every culture, that people want to stay young as long as possible, but the Japanese take it just one step further.

That's just my observation and I'm by no means an expert and if in any way I offended someone, I truly didn't mean it and I apologize in advance! Someone correct me if I'm wrong!

Probably because they haven't done nothing special in their life when they were young.. Like they wasted most of their life.
Older people must feel like they are old and useless.

You're right. it's may be because a young person has much potential than old person. and a lot of workplaces need young ppl than old ppl.

That isn't exactly a Japanese only phenomenon.
The states are filled with people dyeing their hair constantly, getting plastic surgery, and wearing age inappropriate clothing.

Japan actually does better than the US when it comes to old people in my opinion.
In Japan, there may be pressure to get into a company when you are younger when starting off, but due to the traditional corporate structure based on seniority, the older people with the experience are the ones who get promoted.
There is also a built in cultural respect for the wisdom acquired through long life.
The record long life spans of Japanese are a point of pride for them.

In the US, the elderly are much more likely to be the subject of ridicule, abuse, and neglect.

The tendency for females to act "girly" is more having to do with built in Japanese notions of gender roles than age.

Also keep in mind when you are reading manga and watching anime, that you are not observing an exact cultural record.
By their nature, they are usually exaggerated in different ways to provide entertainment.
People don't really talk and act the way you see in many cases.
Some of the characters exist to provide the more restrained Japanese a chance to imagine what it would be like to break out of their set patterns of behavior.
If many of the more boisterous characters existed in real life, they would be looked at like a disruptive and inconsiderate jerk.

I wouldn't have such a problem if it wasn't for the fan service. It's hard to find shows that don't go overboard with it. (and ideally, don't have any)

Japan has america beat in so many ways, it's funny.

You know, I live here and I don't notice much in the way of this obsession with youth as you put it.

Yeah sure, I watch the infomercials and advertisements on television here for a kick and they are always advertising some new silly diet or exercise trend, but then again.. so do the companies in the United States.

They really aren't any more or less obsessed with youth here than they are anywhere else. If anything, the traditional diet keeps Japanese women (and men) looking much younger than their western counterparts because most of the ingredients are natural things like fish, veggies and rice.

True, we have junk food here.. lots and lots of it, but it doesn't make up the staple of the diet here and most people seem to be graceful as they get older, but still maintain a look of youth without overdoing it.

Women here are very culturally attuned to be 'feminine'. However, you probably aren't going to see many women here getting plastic surgery or doing anything drastic outside of the silly diet measures to lose a measly 10 lbs.

Although I did see a ganguro girl last summer walking around the shopping arcade.. the thing that made it hilarious was that this woman was at least my age (older than 20) and had a baby that she was pushing around in its stroller. The image was actually pretty comical.

they like cute things. thats why

Don't all cultures have obsession with youth?
I do not know where you are from but I am from the U.S and in my country people are always talking about youth.
They say things like, " OH~ to be young again, that is the dream".
I don't blame them, I would much rather be young and full of life than to be old and unable to do stuff you would be able to do when you were young. Being young is so over rated, not just Japan : )

Yeah, I was just about to say the same thing. I think youth is a desired thing no matter where you are.

They were deemed illegal about a year ago.