Here's an intriguing question that was asked of retiree investors by the well-known mutual fund company, Vanguard: "If you had a do-over, what would you do differently to prepare for retirement?"

Vanguard received hundreds of answers to that question, and Matt Bell of The Balance highlighted some of the primary areas of concern. These areas provide important insights about retirement worth considering for Boomers, since they reflect the opinions of retirees who have already been through this stage of life.

Investing Earlier
A common theme was that retirees should have considered investing earlier than they did. They recognized that compounding works best over a long period of time.

Investment Decisions
Ill-informed investment decisions were another regret. Clearly, it pays to consider investment decisions wisely instead of risking assets on speculative investments. A related regret was investing too heavily in an employer's stock. When it comes to objective investment decisions, a financial advisor is an important resource.

Social Security
Retirees recognized that it may have been short-sighted to take Social Security payments too early. At the very least, waiting until "full retirement age," or age 70 if possible (when you receive the maximum Social Security monthly payout) makes a real difference in income in later years.

Understanding What Retirement Means
Retirees regretted concentrating on only the financial aspects of retirement. Just as important is the psychological impact of retirement. What you will do in retirement becomes a key challenge, one for which many retirees are unprepared.

Instead of second-guessing your retirement and being unprepared, think carefully about it and plan ahead!

A common characteristic of Boomers is their desire to learn for enjoyment. Education seems to become all the more precious as we age; the popularity of adult education courses through such organizations as OLLI (Osher Lifelong Learning Institute) is evidence of that fact.

Sometimes, though, higher education at an older age serves another more practical purpose: To learn new subjects and skills that are directly applicable to employment. There are obvious challenges in returning to college, but it is a route that is becoming far more common than you might think. The payback is in potentially making yourself a more attractive job candidate.

If you are considering going back to school for job-related purposes, you might want to check out this article:  "The Time is Now: Going Back to School at 50." Posted by Maryville College, which has helped pioneer online college courses, the article discusses reasons you might want to return to college, factors to take into consideration, and degrees and career paths that might be available to you. The article links to a "going back to school checklist" and also points to numerous additional resources. Check it out.

If anyone typifies the adage that you are only as old as you feel, it is Supreme Court Justice Ruth Bader Ginsburg. At age 85, Ginsburg often works through the night and spends an hour a day with a personal trainer on a physical regimen that would put people half her age to shame. She has even overcome two of the most serious forms of cancer, colorectal and pancreatic, as well as the loss of her husband Marty to cancer.

Her story is brilliantly told in the documentary, RBG, that recently ran in select movie theaters. If you missed it, this is definitely a film you want to catch when it hits the streaming market. While the documentary includes the standard biographical overview of a celebrity, it speaks to the wonderful relationship she had with Marty, who supported and encouraged her at a time when women were not supposed to be working, much less as attorneys. RBG highlights the remarkable achievements of this slight, quiet woman from Brooklyn, New York, who as an attorney won five of six cases before the Supreme Court, paving the way for the equal treatment of women in our society.

Another aspect of the film is invigorating: It depicts how Ginsburg has become a virtual cult hero among young women, proving that age is no barrier when it comes to greatness. The film offers insight into the personal life of Ginsburg, too, humanizing a Supreme Court Justice in an intimate, endearing way. We see, for example, the warm friendship Ginsburg had with Antonin Scalia, her polar opposite on the Court, and her ability to laugh at herself while watching a Saturday Night Live skit parodying her.

Whether you are a Ginsburg fan or not, it is hard not to respect and admire her after watching RBG. I highly recommend it.

As a Boomer, you have probably found it useful, at one point or another, to calculate the retirement income you think you will need. Unfortunately, not all of those seemingly handy online retirement calculators are as helpful as they may seem.

According to the Retirement Income Industry Association, some online calculators can offer "extremely misleading" data. That's why it may make a difference to use the right calculator.

This useful article from The Balance evaluates and ranks a number of online calculators on the basis of three key criteria: accuracy, usability, and education. Check it out.

In addition, it should be obvious that an online retirement calculator is just one tool. When it comes to something as important as planning for retirement income, many factors come into play, including Social Security payments, Required Minimum Distributions (RMDs) from retirement accounts, and income taxes. While a calculator can give you a rough idea of what you will need, you'd do best to work with a financial planner to get the complete picture.