marrying first

PARSHAS HASHAVUA (וימת נדב ואביהוא (במדבר ג:ד Some Poskim say that the rule of a younger sibling not marrying before an older one applies only to females. Males who have the Mitzvah of פרו ורבו there is no reason for holding back the Mitzvah because of an older brother is not married yet. ( אג"מ-מהרש"ם) Some want to prove this from נדב ואביהוא. Chazal tell us one of the reasons they were both punished was for staying single and not getting married. If אביהוא would have had to wait for his older brother נדב to get married then why was he punished. This is not really a proof because if the older brother refuses to get married then all agree there is no reason for the younger one to wait Once נדב refused to get married then אביהוא was obligated to get married and yet he didn't, therefore, he too was punished. The ש"ך (Y.D. 244:13) quotes the ב"ח " Both, brothers or sisters should not marry the younger one before the older one". R.Moishe Feinstein zt"l (Igros M. E.H.2:1) says that the ב"ח is only applicable if both are engaged only then must we marry off the older before the younger. A younger sibling (even sister) may get engaged before the older sibling and get married if the older is not engaged yet. The   (מהרש"ם (ח"ג קל"ו  says that this Halacha is not a דין גמור but a Minhag Derech Eretz. Therefore in certain cases ("בעושה משום דחק") it is permitted.