I want to know why  always it is  choosen, groom's age is more than bride's age ?

Is there any scientific and veidic reason ?

if bride is few month elder than groom , is it allowed ?

usually in the family one of couples accept voluntarily submissive position so that other one was able to take position of a dominant person. It is needed, because if two bosses try to stay in one family then life will be like of dogs.

So it is difficult.

Because of that naturally girl accepts submissive position and man in order to give protection for her accepts dominant position.

So it says that girl easily respects a man if he is higher in all area:

...height

....weight

....beauty maybe

....age

....intelligence

....knowledge

....education and so on.

For a woman it will be very easy to respect such like a husband. And respect is the most important thing in the family life.

But if boy is younger than age but more intelligent than girl than it is also nice. 

If girl is older than a boy then she can accept junior role then they will be happy. 

So it depends on girl's ability to respect him or not. 

Your servant,