To start a "modern" project today, you have to know programming languages, infrastructure, and packaging systems that didn't even exist
five years ago.
That's the surface-level "technology" they (VCs) mean. VCs don't care about your deep algorithm knowledge or domain experience unless it can accelerate user-facing interfaces to the moon.
If you hire people with 30 years experience, do they know what a Gruntfile is? Do they know the difference between Gruntfile.js, component.json, and package.json? Do they know the relation between Docker and Vagrant and Kubernetes and CoreOS and rkt and etcd? Maybe they still love XML a little too much. Now they have to re-learn the same things they already knew, but with new fads and new syntax and new bugs built-in, all while trying to keep "old ways" vs "new ways" straight in their cluttered heads.
Even look a hyper-accelerated areas: Ember? Angular? React? React forks? Become an expert in any single one and you're irrelevant within 3 years unless you want to support "legacy" apps forever.
Saying "old" is confusing too. Is "old" 30 years COBOL experience at one company where they wrote everything themselves and can't think any other way? Is "old" 30 years of always chasing the latest fads, master of none?
If you have a long work history, and if you are good at something, there's a good chance soon the thing you're good at will be replaced by something you're not good at. Congratulations, now you are "old" and out of touch. Younger people created something new and now your experience isn't relevant. In a way, "experience" is a fool's game. Experience requires a fixed point of deep understanding, but while you're getting experience, the world is moving out from under you.
You're almost better starting off as a 15 year old who learns everything new with no historical baggage. Nobody wants to hear old stories about stacks of punchcards and time sharing woes when we've got to deploy and monitor 1,000 instances to AWS in the next 15 minutes. But, you can't go back and become a blank-slate 15 year old every 5 years when the fads change out from under you. Ergo, you're old and out of touch and worthless and go live on a programmer retirement farm in iowa because you're not a culture fit with the 22 year old CEOs anymore. yolo, and you wasted it by not becoming a billionaire by 28.