In my experience:
10% techies who can move in and out of contracts and jobs easily
10% blue collars who can also move in and out of jobs easier, particularly if they work for themselves
3% margin of error is reserved for standard office jobs that save up their vacation and "work something out"
This is for the US at least... I do think more people could get extra time off _without pay_, they just don't ask for it. Still, it is sort of depressing when you go to Horizon's Unlimited meeting and the youngest person there is late 40s. (I'm 31)
IMO, if you don't do it now, it probably won't happen. You will get married, have kids, and you probably will want to spend time with them - not going to Cambodia to dirtbike. Kids grow up, you have college costs, you retire - if you live long enough to retire - and realize that life is expensive and you don't have a regular job income anymore and staying in dingy hostels sharing a bathroom with a dozen dirty 20yo hippies and camping kinda sucks.
Not to mention that your experiences will be vastly different at that age. Chances are that you will not be in great shape anymore and you won't be taking 3 days off to trek to the top of some cool mountain in Nepal during your ride, or go skinny dipping with some skanky Dutch girls on vacation in Thailand, etc. Instead, you worry about your X medication/condition and how your kid is doing. Age will limit your experiences. Maybe your experience makes you wiser and you appreciate things more, but you will simply miss out on a lot of random stuff and stories.
The other problem is that the World is Getting Pretty Damn Flat. It is so cheap to fly these days that many places in the World are completely overrun with tourists and that corrupts local cultures. You will go to a lot of places and realize that the only reason why they ride elephants in Thailand or have a silk-weaving village or whatever is to get your tourist dollars and it's not like it was XX years ago when that is what they actually did. Even the poor people in the jungle watch CNN and MTV and it's just not the same and becoming worse and worse each year. In 20-30 years, even fewer authentic places will remain. My personal goal is to check out these cultures and peoples before their identity morphs into a random poor middle America neighborhood.
I don't know if there is a great solution to to your question, but one option is to do Fly & Rides. Fly out on Friday, spent a week riding, and come back Sunday. It is quite a decent option. You are not wasting time riding to get there, and you can cover quite a bit of ground and see a lot during that week. This is why I started a thread that you may find useful and that I hope more people will contribute to: Where in the world can you find cheap bike rentals?