There are nearly 600,000 people who are 100 years old or older in the world, per the United Nations. And that's projected to swell to 3.7 million by 2050.

• The big picture: Our longevity is 25% dependent on genetics, but the other 75% is based on lifestyle choices, The Washington Post's Teddy Amenabar writes.

Here are the top three tips for lengthening life through healthy choices, many of which we've cataloged in Finish Line in the last year.

1. Stay active. Older adults who keep their bodies moving through their favorite forms of exercise, whether it's walking, yoga or dance, tend to stay healthier longer. Check out Finish Line readers' favorite workouts.
2. Keep old friends, and make new ones. A lack of meaningful relationships can chip away at our mental and physical health, especially as we age. Here are pointers on making and maintaining friendships.
3. Go outside. "If I had a jewel to give to people who want to live long and well, I would tell them to get up early in the morning and go out,” Luigi Ferrucci, the scientific director at the National Institute on Aging, told The Post. You can also bring nature inside: Here's how plants make us happier.

The bottom line: We can all take small steps to keep ourselves — and help keep those around us — healthier for longer.

📬 Speaking of healthy aging, thanks to the hundreds of readers in their 70s, 80s and beyond who've sent us their advice on enjoying life's bonus years.

• Keep your wisdom — along with name, age and hometown — coming to [email protected].

"This map reminds me of a great bike tour I took in 2014 during a family trip to Vienna," Finish Line reader Joe K. tells us.

• "I have an interest in Napoleon's military campaigns, and took the opportunity to rent a bike and tour two major battles that took place on the outskirts of Vienna in 1809, the Battle of Aspern-Essling and the Battle of Wagram." 
• "Altogether, it was a 70-mile ride on a beautiful day, very peaceful and satisfying."