Is boy a common noun

Yes, the noun boys is a common noun, the plural form for the noun boy, a Word for any boy anywhere.

A proper noun is the name of a person, place, thing, or a title; for example:

• The Blue Boy, by Thomas Gainsborough
• Boy Island, Temagami, ON, Canada
• Boy Scout Road, East Jewett, NY or Boy Scout Road, Augusta, GA
• "The Boy in the Striped Pyjamas", novel by John Boyne
• "The Boys From Brazil", 1978 movie starring Gregory Peck