Working for a charter airline, I would normally always address a customer as "sir" or "madam" and wouldn't think to address a couple in their forties as "guys." However, I do think when you've got a family of various ages including small children (perhaps not the older generation) or a big group of young people all going on holiday, that "guys" is acceptable. Our airline is almot exclusively taking people to or from their holidays, and hopefully they're in a holiday mood and want to have a familiar and friendly face in the cabin. This is definitely not the case with my last employer, a low-cost airline, who even though flying business routes, encouraged PAs beginning with "Hi/Good morning Folks ..." Cringy.