No, both are adults and do as they wish.
legally no that is basically robbing the cradle, if you know what that means, and why would you want to marry a 18 year old girl if your a 15 year old boy anyway?
No that is illegal.
An 18 year old girl can marry an 18 year old boy even if they are not in love in this state.
A girl should marry between the age 20 to 25 years. A girl should marry one year after regularly meeting the boy whom she loves.
Of-course they can!
In most countries, no.
No.
if they both have parents consent
With parental consent, yes.
Not if the live in Norway.
Not unless he can pay her bride price.
Per Islam teachings, a Muslim boy couldn't marry a Sikh girl. He can marry only a Muslim, Christian, or Jewish girl.