(Image credit: Getty Images) Refinancing student loans is often treated as a milestone: Your income goes up, your rate goes down, and you move on. For high earners , especially physicians and other professionals early in their careers, that moment tends to come quickly. And that's exactly where the mistake happens. Most borrowers don't refinance at the wrong rate. They refinance at the wrong time. From just $107.88 $24.99 for Kiplinger Personal Finance Become a smarter, better informed investor. Subscribe from just $107.88 $24.99, plus get up to 4 Special Issues CLICK FOR FREE ISSUE Sign up for Kiplinger’s Free Newsletters Profit and prosper with the best of expert advice on investing, taxes, retirement, personal finance and more - straight to your e-mail. Profit and prosper with the best of expert advice - straight to your e-mail. The appeal is obvious, and that's the problem Once your income crosses a certain threshold, refinancing feels like a straightforward upgrade. You qualify easily.…