Jacob Girdler joined Roblox on a whim more than a decade ago when he was 9 years old. The entrepreneurial teen, who largely works alone, has now designed over 300 games for the platform.

Roblox has been around for a long time. The online game platform first launched in 2006 — just two years after vanilla World of Warcraft hit (the first time) and three years after Second Life, a ...