Adriana Lima was 28 when she got married
Doutzen was 25
Coca Rocha was 22 and is the only one you mentioned that would be considered young when she got married
You have to remember that many models have been on their own and out of school since they were 16 years old. So while other people are in school until they are 18 or even 22 if they go to university, the majority of top models drop out of school when they are 16. While most people live with their parents until they are at least 18 and are financially supported by their parents at least until they are done with high school if not college, most models become emancipated when they are 15 or 16 and are already living on their own, traveling the world, and working to support themselves financially. So they mature faster than most other people.
Since Coca Rocha has been on her own since she was 16, living in NYC, and working for 6 years before she got married, it's really no different than someone who was supported by their parents and going to college until they were 21 or 22, then worked for 6 years and got married at 26 or 27
EDIT - regarding money, Adriana Lima earns more money per year than her husband and her modeling career is going to last longer than his basketball career. Doutzen makes MILLIONS more than her husband who is a DJ and not even a world famous one. Coca Rocha's husband is an interior decorator who doesn't make anywhere near what she earns. She makes more money on a single Dior ad than he probably earns in a year. They are not marrying young to snag an old rich man - all three of them married men earning LESS money