More than four million people are expected to retire this year, with the average age of retirement at 64 years old.

On average, people will spend a third of their life at work. That adds up to 90,000 hours, and that leaves most dreaming about the day they don't have to clock-in.

"You have built a family, you have built a career, you've built a life, and now you get to reap the benefits of those things," licensed mental health therapist Christine Hammond said.

A study by the Mass Mutual Retirement Institute found that retirees with a strong sense of purpose are more likely to feel happy, healthy and fulfilled.

But how do you get there?

The first step, plan early and find new interests before you leave your job.  

"Something that you've wanted to do and go try it and just say, you know what, I'm just going to try this for six months and then if I don't like it, I'm going to move on to something else," Hammond said.

Don't give up on goals. Set personal milestones that give your days a sense of direction.

Also, be sure to engage with others. Join clubs, volunteer, or take up a group hobby.

Twenty-five percent of those 65 and older are socially isolated. Connection helps bolster mental and physical health.

If you just love to work, consider an encore career. Encore careers provide seniors opportunities to pursue work that aligns with their values and interests.

Also, don't be afraid to pass on what you've learned. Mentoring younger people, can boost your self-esteem and satisfaction of life.

"This is the age of wisdom for them where they can take all of their experience that they have gained throughout the years, and they can like impart that knowledge onto other people," Hammond said.

Remember, retirement is a chance to reinvent yourself, explore uncharted territories, and leave a lasting impact.

Stay active. The CDC says older adults need 150 minutes of moderate-intensity aerobic activity each week. Working out over 65 lowers your risk of heart disease, stroke and some types of cancer.

Also, be sure to stay in touch with the younger generations.

Intergenerational relationships are good for the soul, not to mention another way to stay connected and combat the health consequences of loneliness. It allows both parties to learn from each other and gain a broader perspective.

It also helps older adults impart their wisdom in a way that gives them purpose.