They said don't expected that your bf who younger than you will take care of you. coz your younger bf is still young .His life just started and he has full energy to build future.he has so many things to do But if your bf is older than you, his life passed everything and almost done. he will stops at you. he want to be with you. if you are dating with younger man than you . It's natural of older sister will take care of younger brother .