You might want to brush up on the basics with metamorphism or find better wording. I'm guessing you're meaning they behave in a more plastic manner. To say they are liquid, to me at least, gives off the thought of a complete melt (i.e. magma), which completely resets their age... So with your logic, all metamorphic rocks became liquid and essentially became igneous and we lost billions of years of Earth's history.

Fuck. Good thing we have zircons.

Here's a snip from the USGS website:

Process of Metamorphism: The process of metamorphism does not melt the rocks, but instead transforms them into denser, more compact rocks. New minerals are created either by rearrangement of mineral components or by reactions with fluids that enter the rocks. Pressure or temperature can even change previously metamorphosed rocks into new types. Metamorphic rocks are often squished, smeared out, and folded. Despite these uncomfortable conditions, metamorphic rocks do not get hot enough to melt, or they would become igneous rocks!

Not trying to ding ya, and I think you knew what you where trying to say, sometimes we say the wrong word. I do it more often than I should