fertilization age vs gestational age

fertilization age and gestational age both are nouns.

Word	Noun	Adjective	Verb	Adverb
fertilization age	Yes	No	No	No
gestational age	Yes	No	No	No

As nouns, fertilization age and gestational age are synonyms defined as:

fertilization age and gestational age: the age of an embryo counting from the time of fertilization

Other synonyms of fertilization age include fetal age.

fertilization age (noun)	gestational age (noun)
the age of an embryo counting from the time of fertilization	the age of an embryo counting from the time of fertilization