4 cornerstones of retirement planning

On average, 60-year-old Americans can expect to live another 20 or 25 years, depending on their gender and other variables. And most baby boomers can also count on a couple of extra years free of disease and disability compared to 60-year-olds of just 15 years ago due to improved medical treatments, according to a study from Harvard University.

So how can we make the most out of our ever-lengthening lives? Here are four cornerstones to a healthy, positive retirement.

[Read: How to Estimate Your Life Expectancy.]

1. Get a handle on how long you're going to live, because it might be longer than you think. Life expectancy figures offer an average, but they do not tell your personal story. Adjust your own possibilities by how long your parents lived, what your lifestyle is and your own personal history. There are a number of longevity predictors that ask questions and predict your lifespan. For the most part it's obvious. The healthier you are, the longer you'll probably live. But even for an average 65-year-old couple, the man could live another 20 years and the woman has a decent chance to survive to age 90.

Once you get a sense of how many years you have, you can better figure out your plans. This is how long your retirement assets have to last. But it can also help you decide what activities you want to pursue, where you want to live and what goals you can expect to achieve in retirement.

Check out the average retirement age in every state:

2. What are you going to do? There are more opportunities than you think. Since you'll be spending 20 or 30 years in retirement – almost as long as you spent in your career – it's important to make retirement satisfying and fulfilling. You may have long-held interests and can map out what you want to do. But there is also time to experiment or change your priorities. You may start out hiking the Pacific Crest Trail, but end up volunteering in your community or raising grandchildren. Regardless, you need to ask yourself some questions. Do you want to stay in your current home, downsize to smaller quarters or strike out for a retirement mecca? Do you want to keep working, perhaps at a part-time job or developing a hobby that allows you to earn extra income?

[See: 12 Financial Terms Every Retirement Saver Should Know.]

The main idea is to remain active in some shape or form. The more you see retirement as a time to seek out new opportunities, the more likely those extra years will be enjoyable and rewarding. Use this opportunity to choose activities that speak to your own passions, not the expectations of parents, family or the workplace.

3. Hold on to old friends, make new ones and build your support system. Research shows that retirees who have friends and spend time with family are happier and more satisfied. According to the Pew Research Center, a majority of people over age 65 see spending time with family as one of the most rewarding aspects of aging. Married seniors with children are happier than those who are not married. Yet singles often compensate by spending more time with friends, and seniors with good friends are happier than those who don't have enough friends. Women typically have more friends than men. Some 80 percent of older women, versus 65 percent of men, say they have people they can turn to when they have a problem, Pew found.

[See: 10 Social Security Rules Everyone Should Know.]

4. Make sure to have a handle on your retirement finances. A longer, healthier retirement is a good thing. But the benefits may seem hollow if you're constantly worried about money. That's why it's important to have a sound, long-term strategy to provide retirement income that will last as long as you do.

You should know what your reliable monthly income is from Social Security and pensions as well as any extra money you can access from a savings account, part-time job or other source. A budget can outline your monthly expenses, including essential ones like food and housing as well as discretionary costs like travel and entertainment. It's up to you to balance your wants and needs with your various resources and decide where you have opportunities to expand income or how you can pare back spending if you have to. If you understand your financial situation, you aren't helpless if a nasty surprise upends your life. You can instead make your own decisions, pull the appropriate levers and control your own destiny.

See the 10 best states for retirement in 2016:

Tom Sightings is the author of "You Only Retire Once" and blogs at Sightings at 60.

Copyright 2016 U.S. News & World Report