This is a persistent myth, but if you examine the math it doesn't work out. A VC firm could improve their returns by at most 2x or 3x by extracting really good terms from an inexperienced founder. But that's rounding error compared to the 100x difference between a big success and a small one.
This is a subset of the more general rule that there is no "value investing" in startups. All the returns are concentrated in a few big hits, and a VC does well iff they invest in them, regardless of the terms.
The empirical evidence confirms this. Google and Facebook are among the biggest recent hits for VCs. Both had young founders. But the reason VCs made so much from these deals is not that they extracted unusually good terms from the founders. In fact, the founders extracted unusually good terms from the VCs. The VCs made a lot despite that, because the companies were so successful.