Of-course they can!
Yes he can marry with 19 year old Nepali girl and after this she can also get citizenship of india.
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.
In most countries, no.
In Islam , a muslim is not allowed to marry a hindu girl , but a muslim can marry Ahle Kitab i.e. a christian or jewish girl .
No Mehra Sikh girl cant marry a sasan boy .Sikh Mehra[Kashyap Rajput] caste is well known caste and its a General caste all over India
No.
if they both have parents consent
With parental consent, yes.
Not if the live in Norway.