How much are you making? What industry are you in? Where do you live? Is your income stable or volatile?
I charged a $250k rate ($125/hr) as a contract front-end developer based in SF for years. I worked exclusively for startups, and I worked remote more than 50% of the time.
My income was stable. I never had any downtime between contracts, and I often turned down work. I only had "light" months when I took vacations. Some months I made as much as $30-40k.
How long/What did it take to get to your level? What kind of work do you do? Do you enjoy it, or is it the stereotypical "highly paid because it's crappy" work?
I started as a web developer in college and I had contracts where I charged $60/hr. I didn't start charging $125/hr until I was 26.
I genuinely enjoyed the work I was doing. I only took gigs where I'd have a lot of creative license. More than a few times, I was the only front-end developer on the team. Sometimes I was the designer, too.
Is this a short-lived opportunity, or do you expect it to exist in 5 years?
Depends on the supply and demand of the startup economy: how many startups there are, how much funding they're getting, and how many good developers there are. Things seem like they're going strong, though. Last year I taught a smart friend of mine to code. She got a job making $100/hr in January. In hindsight, I probably could've charged more than $125/hr :D
Personally, I'm done with contracting. I really like the idea of running my own businesses/projects that generate regular income. Currently I'm working on https://IndieHackers.com. Not only is it a business for myself, but it also helps other with the same goal. I think being independent is the future of work for programmers.
What would your advice be to a 25-yr-old aspiring developer? 30? 35 ?
Don't become complacent. Never stop learning. Keep working on side projects and releasing them into the world. Almost all of my contract jobs were inbound requests that came when people saw my projects and wanted something similar for themselves.