Nikkah

Hira asked 2 years ago

Asalamu alaikum. I am a muslim born female pursuing a relationship with a non-muslim male. He is interested in converting so that we may spend our lives together as husband and wife. Our main problem is finding common ground on when to marry/have a nikkah because in his background, people take years to get to know each other before advancing while in Muslim culture, people often get married quickly to avoid any sins.
We are still young, both of us are in university so we want to wait a little bit (about 1-2 years) before we have a wedding ceremony. But, I was wondering if a nikkah can be done before without any legal husband and wife documents, so that we are able to spend as much time together without worrying about committing sin. Are we allowed to have a small religious ceremony without being legally married? My mother insists to do both at the same time and says a nikkah without the legal marriage documents is not allowed and I would like to clear this up. 
 
Thank you