On Roblox, old and new coexist. It’s an interesting manifestation of the company’s ethos, and one reflected in the decisions Roblox makes with its underlying technology.

And among the 8- to -14-year-old set, Roblox is doing big business. CEO David Baszuck told me he's recording 19 million play hours a month from 5.7 million unique users.

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. One of ...