If you already have a good source of income doing a stress-free job that you enjoy, then you are already ahead of most people on this planet. If your goal is to open up your own studio, you’re going to be living a very different life. You will be stressed out all the time, and you will be dealing with a lot of business end of things that have nothing to do with creativity (unless you can afford to hire/partner with someone to do all that–basically run your company for you while you just handle the creative aspects). And you’ll likely find that your work life will completely dominate your personal life, because running a company is so much work.
Now, about your desire to become a good concept artist.
What is your motivation? Do you actually love the process of drawing/painting/designing? Don’t think about anything else (what you’ll be using the concept art for)–just focus on the actual process of brainstorming and researching design ideas for environments, characters, vehicles, weapons, gadgets, creatures, etc, and then sketch iteration after iteration of different variants to explore possibilities, then draw/paint it to the level that is considered top-quality work, which will take many hours of hardcore drawing/painting. Do you have any experience going through that entire process? How much of it have you done so far? And did you really LOVE the process, or did it feel like a chore?
See, you have to separate your desire to do something from whether or not you actually love doing it. There are way too many people in this world whose desires are writing checks their personality can’t cash. I have taught hundred of students, and many of them wanted to be concept artists, but when it comes to actually putting their noses to the grindstone and actually putting in the hard work, many of them discover that they had the desire, but lack the personality for it (meaning they lack the discipline, patience, tenacity, endurance for hardship, and the ability to enjoy being challenged and fighting hard to become better). This is the difference between talking the talk and walking the walk.
When you really love the process itself, it doesn’t even feel like hard work, because you just lose yourself in the endeavor and that full immersion makes it easy to endure the many hours, days, weeks, months, and years of pushing yourself to the limits of your ability. But if you find the process too grueling and it feels more like torture and a chore, then you are desiring something that your personality isn’t suited for.
Whether you make a living with your art isn’t a real indication of how good you can be, but generally speaking, professional are so good because they need to be that good in order to compete and make a living, so there’s extra incentive on top of them being passionate and loving what they do. So unless you make your artistic development into something that is just as all-consuming and demanding of your time and energy and dedication, it’ll be very difficult to reach the same level as the professionals.
Assuming you have the right personality, love the process, and you have the passion, discipline, tenacity, intelligence, curiosity, imagination, and endurance, then yes, you will be able to become a good concept artist if you work very hard at it the way full-time concept art students do while attending a demanding art school like The Art Center in Pasadena. There are enough learning resources out there these days that you can design a full curriculum for self-learning and achieve your goal.
One thing to keep in mind, is that when it comes to excelling in any creative endeavor, it often requires you give all you’ve got (or close to it). It’s not as if you only give 50% of your passion and dedication, you’ll see a 50% yield. It’s more like there’s a threshold you have to meet (let’s say maybe 85% minimum), and if you don’t meet that threshold, then all of your efforts will end up resulting in not much of anything, because you haven’t built up enough momentum to see clear results of your hard-work, and without that momentum, you will lose interest, and then give up. And you have to keep the momentum going, because you could be one year into your artistic development and then lose your momentum and it all just ends right there. Once you lose it, it’s very hard to get it back. Many people lose their momentum when they’re young, and only with age and mounting regret manage to find the motivation to try again many years later.
And to echo what other said–26 is still very young. There are many of us who would trade something very valuable–like a body part, to be 26 again (but still retaining the experience/wisdom we’ve built up at our current age).