元気な 人 ← correct.
(adjective)(noun)
元気(genki) 人(hito) ← wrong.
(noun) (noun)
元気人(genki jin/bito) ← as a slang or a unique noun, it's okay.
Actually, according to some dictionaries or a grammar site, 元気 is a noun/an adjective verb(形容動詞)/an adjective, but 元気 is a noun, 元気だ is a 形容動詞,
"元気 itself is an adjective" is wrong information.