Hi Christine

Historically speaking, I would say that Sri Yantra is many centuries old,
and that Metatron's Cube cannot be traced back more that a few centuries.

However, mythologically speaking, it depends on your belief system.
Some would say Sri Yantra is the primal vibration that created the universe.
Some would say that Metatron's Cube is the blueprint of creation.

Sri Yantra represents a vibrational energetic field.
Metatron's Cube represents the building blocks of material form.

Which one is older? Perhaps both are older than time itself...