SAN FRANCISCO — For years, job hunting over the age of 40 in the youth-obsessed Silicon Valley could prove hazardous to your career.

But judging from the experiences of technology workers roaming the country in search of job opportunities elsewhere, ageism is a universal problem in the industry.

“It’s not just Silicon Valley. It is everywhere,” says Pete Denes, 59, who used to run a $200 million sales division at Hitachi and now sells yard and monument signs in his native Omaha after a go at real estate in Phoenix. “It is very frustrating after a while.”

From California to Arizona and now Omaha, Denes says he traveled far and wide in search of work in tech.  Nearly a decade and 300 rejected resumes later, he concluded it’s “virtually impossible to get my foot in the door anywhere.”

His experience is becoming increasingly common.

Age is the silent career killer in the tech industry. While companies openly wrestle with the lack of racial and gender diversity, regularly releasing workforce demographics, they refuse to disclose the average age of their staffers and offer little in the way of internal support for older workers.

A rise in complaints, and lawsuits, over ageism in Silicon Valley and elsewhere the past few years has contributed to the reticence among major tech employers to speak up on the topic.

“Systemic issues contribute to tech and (non-tech) fields,” says Brooks Holtom, management professor at Georgetown’s McDonough School of Business.

In tech, the issue is pronounced, he says, because start-ups are “based on young people taking risks, paying entry-level wages, to start companies.”

The median age of an American worker is 42. Yet at Facebook it’s 29, Google 30, Apple 31, Amazon 30 and Microsoft 33, according to self-reported employee data collected by research firm PayScale last year. (It did not collect data this year.) Most job candidates at those companies are 25 to 34 years old, according to data collected by Glassdoor, a jobs and recruiting website.

As the population ages, discrimination in hiring and on the job is becoming more pronounced not only in Silicon Valley but in tech hubs throughout the U.S., where workers relocated from the San Francisco Bay Area…