The Jamaican currently holds world records in the 100m, 200m and 4x100m with times of 9.58s, 19.19s and 36.84s respectively
The 21-year-old founded and owns Kylie Cosmetics, the three-year-old beauty business that generated an estimated $360m in sales last year, reports bbc.com.
She reached the milestone earlier than Facebook founder Mark Zuckerberg who became a billionaire aged 23.
"I didn't expect anything. I did not foresee the future. But (the recognition) feels really good. That's a nice pat on the back," Kylie told Forbes.
The list shows Amazon's founder, Jeff Bezos, remains the world's richest man.
His fortune totals $131b, according to Forbes, up $19b from 2018. But the billionaires' combined worth is down from $9.1 trillion at $8.7t.
Facebook founder Mark Zuckerberg's wealth is among those falling. It has dropped by $8.7 billion in the past year to $62.3 billion, according to the Forbes list.
His shares in Facebook at one point lost a third of their value as the company battled privacy scandals.
Of all the billionaires on the list only 252 are women, and the richest self-made woman is real estate mogul Wu Yajun of China, worth an estimated $9.4 billion.
The number of self-made women reached 72 for the first time, up from 56 a year ago.
The Jamaican currently holds world records in the 100m, 200m and 4x100m with times of 9.58s, 19.19s and 36.84s respectively
Total property income posted year-on-year growth of 10% to $74m, highest value ever
All official donation channels however remain open through the outlets announced by government agencies
The Starlight Park is a four-building freehold community in Meydan
The 22-time major champion admits his farewell tour hasn't been as enjoyable as he would have hoped
Eating out, poor hand hygiene and erratic weather may be among causes, say medics
The goal-scoring striker is suffering from a muscle injury sustained during the Champions League quarter-final loss to Real Madrid
Lieutenant General Abdullah Khalifa Al Marri, Commander-in-Chief of Dubai Police, made the announcement on Wednesday