life style vs fast lane

life style and fast lane both are nouns.

Word	Noun	Adjective	Verb	Adverb
life style	Yes	No	No	No
fast lane	Yes	No	No	No

As nouns, fast lane is a hyponym of life style; that is, fast lane is a word with a more specific, narrower meaning than life style:

life style: a manner of living that reflects the person's values and attitudes
fast lane: a hectic and pressured lifestyle often characterized by recklessness or dissipation

Other hyponyms of life style include free living, vanity fair, nomadism, settledness.

life style (noun)	fast lane (noun)
a manner of living that reflects the person's values and attitudes	the traffic lane for vehicles that are moving rapidly
	a hectic and pressured lifestyle often characterized by recklessness or dissipation