Brendan Foody had just finished his sophomore year at Georgetown University in 2023 when he dropped out to jump into the artificial intelligence fray in San Francisco.

Karun Kaushik dropped out of the Massachusetts Institute of Technology that year to move to California after constructing an A.I. tool in his dorm room. And Jaspar Carmichael-Jack, who was traveling the world after high school, had the same idea in 2022.

Now Mr. Foody, 22, Mr. Kaushik, 21, and Mr. Carmichael-Jack, 23, are each running A.I. start-ups within a 30-minute walk of one another in San Francisco. They have raised millions of dollars for their businesses and are supervising dozens of employees. They all have a dream that their companies will make it big.

“When ChatGPT came out, it was so clear to me that this is obviously going to be a paradigm shift,” said Mr. Carmichael-Jack, the chief executive of Artisan, which makes an A.I. sales assistant and has raised more than $35 million in funding. “I knew I wanted to be involved in that.”

The entrepreneurs are part of a fast-growing cohort of chief executives in their 20s who have flocked to San Francisco’s A.I. boom.