The fact is 18-29 year olds don't have the time or money for something like this. I'm 27 years old and I make very good money, but could not find the time to fly to Japan (from the US) to visit and if I had the time, I probably couldn't afford to do it.
I agree with others that it's not about the money or "time" here in Europe (Finland at least). I'm 20 myself and have done a lot of traveling in Asia and around Europe, sometimes alone and sometimes with friends. In fact in two weeks I'll be traveling to Asia for few weeks. This time I couldn't get anyone (of my friends) to join me, as most of them are in the military.
But like I said, it's not about the money. The flights are the biggest expense but there are bargains out there, like few years ago when Ryanair had 10 euro round-trip fare to Dublin. Long-haul flights are of course more expensive, but it's not too difficult to find round trip fares that cost less than 600euros. Aeroflot anyone?

(Actually some time ago Lufthansa offered flights from Helsinki to Tokyo for 550 euros ). Finland is very expensive country to live in and I've noticed that often when I leave my house I easily spend over 50 euros to something useless (like alcohol

). That same 50 euros equals for two (or more) days in SE-Asia including accommodation.
Where do I/we get the money from? Well, I usually
work hard during summers or after school and try to
save as much as I can and because I still
live in home, I don't have to worry about paying for rent or food. Oh, and I don't own a car, which is a big one if you want to save money. I was an exchange student in USA few years ago and couldn't help but notice that every teen had their own car.

But in addition to the salary from the work I have to give credit to my
grandparents because they are very generous.

And of course to the Government as well, because they always "over tax". Though it's nice to get some money back a year after.

This December I'll be getting a check of 400 euros as
tax refund.
Of course this changes a little bit after I move on my own, but I'm positive that I'll keep traveling, I just have to save harder and spend less.
Interesting article concerning vacation in USA. This clarifies why we have time to travel and you don't.
http://edition.cnn.com/2011/TRAVEL/05/23/vacation.in.america/index.html But that's enough of off-topic. I voted "no", because I like to travel on my own. I could never travel on a group which has a schedule of some kind, because planning the trip is half of the fun! I always do a throughout research about the culture and history (and often language) of the destination where I'm traveling anyway so that I can enjoy the holiday even more.