I actually agree with you. Your average 20-somethings lucky enough to be making $70k are too scared to give it up for a few years in this economy where most of their friends are underemployed. Your average 30 & 40 somethings sail after work and on weekends/vacation within in a few hundred miles of home because they have burdoned themselves with kids, careers, and responsibilities. I think these are big reasons the "average" cruisers are in their 50s & 60s.
I have no idea who decided that $70k per year was what is required to be able to sail, was there a meeting I missed? I think that most people who are actually cruising the world are making a WHOLE lot less than $70k per year, in fact I bet they are making not much at all.
You can buy a boat for under $20k that will do just fine, you will have to work on it, and fix it up a bit, but when there are many boats between $3,000.00 and $15,000.00 USD out there that are capable boats that just need some work on them along the way, a young person who is not married and tied down yet has a better chance of cruising the world than a 30 something with a great job.
Most of the people I actually know in the flesh who cruise, some who have done circumnavigations, do it on boats most of us would be afraid to get on, but they do it and it seems to work. You do not here of hundreds of little boats lost at sea every month, so they must be floating somewhere.
Once again, the key to living a dream is to work and make your dream come true, that is not subject to any age restrictions. There are people on here who have celebrated seven decades of life who are looking for a girlfriend to go sailing the world with them, and people who have not yet made two decades who are doing the same. I think the main ingredient for success in this lifestyle is something that cannot be quantified in a resume, it is called gumption, balls, fortitude, bravery, fearlessness and many other things, but what I like to call it is a spirit of adventure.
Many things in life require risk to attain them, wealth is one of them, true wealth is not earned by an hourly wage, it is earned by investing in dreams.