There are several reasons younger developers are sometimes valued over older candidates. Work life balance is part of it, but there are other factors at play. This is a pretty well trodden topic, and you can find a lot of the typical discussion points by Googling. A common explanation, for instance, is that experience in tech doesn't accrue a ton of value due to tech obsolescence - 20 Cobol experience doesn't really translate to much of anything these days.

However, rather than re-hash all that, it's worth taking a look at the numbers - numbers that absolutely indicate a younger skewing workforce. For instance, the average age at Facebook is 26, and 31 at Google. Tech as a whole leans young, with the "oldest" tech company workforce (HP) still younger than the national median [1]

Now, whether simply having a younger workforce points towards actual age discrimination is a matter of fair debate. A perfectly reasonable explanation might be that tech is a young field, hence a young workforce. However, there are enough confounding factors (limitations of experience, work/life balance in dev roles, etc.) that certainly make for rational arguments in favor of age being more of burden than boon.

Then, of course, you have stuff like this :

> "Young people are just smarter. Why are most chess masters under 30? I don't know. Young people just have simpler lives. We may not own a car. We may not have family. Simplicity in life allows you to focus on what's important." -- Zuckerberg

True or not, it would be weird to argue that his opinion is somehow a rare isolated outlier. It speaks to a common conception - both in the valley and in tech - that this is a business for the young.

[1] http://bits.blogs.nytimes.com/2013/07/05/technology-workers-...