root system vs rootage

root system and rootage both are nouns.

Word	Noun	Adjective	Verb	Adverb
root system	Yes	No	No	No
rootage	Yes	No	No	No

As nouns, root system and rootage are synonyms defined as:

root system (noun)	rootage (noun)
a developed system of roots	the place where something begins, where it springs into being
	a developed system of roots
	fixedness by or as if by roots