old-timer vs expert

old-timer and expert both are nouns.

Word	Noun	Adjective	Verb	Adverb
old-timer	Yes	No	No	No
expert	Yes	Yes	No	No

As nouns, expert is a hypernym of old-timer; that is, expert is a word with a broader meaning than old-timer:

old-timer: an experienced person who has been through many battles; someone who has given long service
expert: a person with special knowledge or ability who performs skillfully

old-timer (noun)	expert (noun)
an elderly man	a person with special knowledge or ability who performs skillfully
an experienced person who has been through many battles; someone who has given long service

old-timer (adjective)	expert (adjective)
	having or showing knowledge and skill and aptitude
	of or relating to or requiring special knowledge to be understood