Travelers 18 and older are welcome aboard Viking's adults-only ships, which feature destination-focused itineraries around the world.
Hop across the pond to sail on U.K.-based Saga Cruises, which specifically caters to guests 50 and older though travelers may bring a companion as young as 40.
Two ships in P&O Cruises' U.K.-based fleet – Arcadia and Aurora – are exclusively for adults 18 and older.
Azamara's four upscale boutique ships provide immersive travel experiences geared toward adults.
Scenic Eclipse, touted as "The World's First Discovery Yacht," offers an all-inclusive, ultra-luxurious experience for just 228 guests with 172 crew.
This cruise line has five luxury vessels in its fleet – with the sixth ship, Seven Seas Grandeur, set to launch in November 2023.