One Piece manga targeting younger generation or not, I don't think it's logically make sense for adventure obsessed Luffy to settle down at one island and have a family of his own. There is no requirement that pirate crews must be disband after achieving their goal, Roger was special case cause his disease and even then he at least sailed for 20+ years
Also while I really love Luffy x Vivi, I don't really consider that something that will come true, infact I don't think any ship will actually happen and one piece will end with no one getting married. Open to reader interpretation what they want to think.