First of all the 10K-hour rule is pretty bullshit. Not all hours are equal. It's all a sliding scale with diminishing returns. Also there's no minimum level of

First of all the 10K-hour rule is pretty bullshit. Not all hours are equal. It's all a sliding scale with diminishing returns. Also there's no minimum level of expertise to reach your career goals. Like in body-building, the initial efforts for an untrained person pays off dramatically more than later effort. See the 80/20 rule. You can definitely switch careers at any age. But you also should think about it in terms of both personal satisfaction and opportunity costs. There's a tendency to think the grass will be greener in the new career. That may not be true, most generally available work has large unsatisfying components - otherwise you wouldn't need to pay people to do it. The other thing is opportunity costs. If your new career requires losing 4 years of income while you do an undergraduate degree, plus paying for said degree, then you're 48 and have maybe 17 working years left until retirement (varies, but just an example) then you have to think if you wouldn't just make more money in your existing career, with less risk. Money might not be your primary objective here, but it often is. Also could your family afford for you to be earning negative income (paying for training) while retraining, for the duration required? There's no one-size fits all advice. Just don't rule it out because of your age. Do the math and be logical, not emotional, about it. Get some friends to check your math, because they will be more impartial than you.