The gap sounds plausible, but I highly doubt the overall positions relative to 0.

E.g., the Federal Republic of Germany has had conservative chancellors for 51 years out of the 75 since it was founded. We did not have a constant left majority (I assume that is what they mean by liberal, since the actual sense of the term doesn't make sense as an opposite to "conservative").

Edit: I fucked up, this is only about people below 30.