Clearly he was "older" than Ruth ("You have not run after the younger men, whether rich or poor" 3:10b), but that surely does not necessitate him being "old."
Only God could engineer such grace and generosity.
Bingo! You have cut to the chase. That's why I like the book of Daniel so much, because it so aptly illustrates that, ultimately, God is in complete control. Then, like you, I notice the same thing in the other books.
Young men: 20-30 Manhood starts at 20. Fully grown is 30, when the priest may begin working as a priest.
Boaz: 40-50 or more. He’s related to Elimelech. Younger brother? Cousin? There’s someone closer. Another brother? Another cousin?
Ruth is probably 25-35, having been married 5-10 years.
I find it fascinating the Bible doesn’t reveal his relationship to Elimelech, nor the name or relationship of the closer relative.
Beggin’ yer pardon, perfessor; but painting #1 by Rembrandt depicts Boaz looking older than Joe Biden.