Age when their business started:  

🇺🇸 Bill Gates (Microsoft) - 19
🇺🇸 Mark Zuckerberg (Facebook) - 19 
🇺🇸 Walt Disney (Disney) - 21 
🇺🇸 Steve Jobs (Apple) - 21
🇮🇳 Ritesh Agarwal (OYO) - 22
🇺🇸 Bill Clerico (WePay) - 22
🇺🇸 Jack Dorsey (Twitter) - 23
🇺🇸 Larry Page (Google) - 25
🇺🇸 Sergey Brin (Google) - 25
🇮🇳 Dhirajlal Ambani (Reliance) - 25
🇨🇳 Jack Ma (Alibaba) - 29
🇺🇸 Elon Musk (SpaceX) - 30
🇺🇸 Jeff Bezos (Amazon) - 30
🇺🇸 Henry Ford (Ford) - 39 
🇺🇸 Vera Wang (Vera Wang) - 40 
🇺🇸 Jeffrey Brotman (Costco) - 40
🇺🇸 Robert Noyce (Intel) - 41
🇺🇸 John Warnock (Adobe) - 42
🇺🇸 Ralph Roberts (Comcast) - 43
🇺🇸 Donald Fisher (The Gap) - 44
🇺🇸 Sam Walton (Walmart) - 44 
🇺🇸 Bob Parsons (GoDaddy) - 47
🇺🇸 Bernie Marcus (Home Depot) - 49
🇺🇸 Gary Burrell (Garmin) - 52
🇨🇭 Henri Nestlé (Nestle) - 52
🇺🇸 Ray Kroc (McDonalds) - 52
🇮🇳 J. C. Mahindra (Mahindra) - 53