My sense after meeting hundreds of cruisers (mostly circumnavigating) is that there are precious few people in the their 40s and early 50s cruising. A substantial majority are retired folks from 55 to 80, the next largest group were 25 to 33. They were off for a three year adventure before returning home to go back to work.
At age 47 my wife and I are in that minority. As a rule we are generally either the youngest couple in a social group, or the oldest...
In our case its a matter of planning ahead, amassing assets and so on. We were fortunate in career choices, and we planned accordingly - we could not have done this without a lot of income in our 30's and 40's. At least not in this boat and level of comfort.
Unfortunately no plan survives contact with the enemy and ours has not. We bought our boat in 2006 with plans to leave "around 2009, after the house sold". We had to decide between waiting longer for the house to sell or cruising with our kids. After the house was on the market too long and our oldest was heading into high school we decided to damn the torpedoes and get out there cruising with them before we missed the opportunity forever so we left in 2012 with a house still on the market.
After all, what was the "worst case?" Two years out and we still have the stupid money sucking house? Never happen, we can just dump the price, right? Fast forward two years...and we're damned close to a buyer! Seriously. But we've few regrets (yet...), the two years with the kids has been priceless. We couldn't have left in 2014 with a Senior in high school.
It remains to be seen how well "The Plan" will hold together through two college educations, two extra years of home ownership, and all the rest. We could certainly do this cheaper, and likely will at some point in the future by moving to a smaller boat when we don't have kids on board any more.
But the point is it takes some planning, no matter your income or planned cruising lifestyle. You need to learn about finances and money and how to make more money with it. And think long and hard about how your money is spent today, in your non-cruising, cash-flush existence and down the road when your bank account doesn't get refreshed with a paycheck every week or so.
One thing we did the last year was try to spend more like we would on the boat. With lots of income its tempting to go out to dinner, drop $5-6 on coffee at the drive throughout day, still buy a $10-15 bottle of wine on impulse - all the sloppy financial habits you get into when you know there is more money coming in.
For the last twelve months before we left we scaled that back, a lot more than we had already done, and I wished we'd done it many years earlier. Even stupid things, like getting my coffee at Cumby's ($.99) versus Dunkin' ($2.79? - that was ~$1,000 saved) and setting a "$10 rule" on wine (since cruising reduced to a "$5 rule") and switching from premium brands to less expensive (No more Bombay Sapphire, but I discovered I liked New Amsterdam better at 1/3 the price) choices cut out a lot of fat. Never mind cutting dramatically on dinners out, convenience food, delivery pizza & Chinese and so on. And buying strictly what was on sale at the grocery and planning meals around that while aiming at less expensive food choices in general. And looking long and hard at various reward programs, incentives, coupons and other things that are either costing money for little value or generating value we'd never taken full advantage of.
Good prep for a fixed income life, I learned to revel in frugality and savings.