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.
Your fascination with the Bible's omissions bespeaks your thoughtfulness in considering the text. Nothing is either included or excluded by chance, of course; to me, it is one of the most wonderful parts of Bible study to, well, wonder about those things, and others similarly. Along with other things, I hope during the Millennium we'll learn about all those gaps.