fertilization age vs fetal age

fertilization age and fetal age both are nouns.

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

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

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

Other synonyms of fertilization age include gestational age.

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