I guess if you have well-behaved and disciplined people below 30 things might work in favor of them, but the majority of developers I meet in daily life refuse

I guess if you have well-behaved and disciplined people below 30 things might work in favor of them, but the majority of developers I meet in daily life refuse to grow up any time before their 30s. Long days? Sure. Get the product shipped within spec and on time? If they don't get distracted. But that might only be problem in the West.