Nnnnno. They can't. 'Boy' is a word that means 'juvenile male'. Males don't menstruate. So no, boys can't have periods. Maybe you've got some post-modernist bullshit redefinition of 'boy' that actually applies to girls? Don't wanna hear it. Words have meanings. Reality is objective. Male is not female. Female is not male. So save that shit for some dumb sucker gullible enough to fall for it.