Why the profit margin is low in islamic banking system as compared to convential banking system ? and if a person is retired from a job and he is 60 years old and he has some amount that he want to invest to run his family so he needs large profit to run his family... so what shold he do ? or the profit or interest from the bank or any financial institution is haraam or halaal for that person who is 60 years old? so can he invest in commercial banks? give answer with the help of islamic shariah(principles)