We are classmates and after 1yr we completing graduation and thinking of convincing our parents but I know it would be too difficult to convince them so help me out.

Need some more information... if the parents are devoted in their religion, it's unlikely they will change,being older.
I imagine that they will say you are very young to make this kind of change in your life.

If you can't at least try, why even think of marriage?

Just curious, are you talking of graduation from High School or College.

That makes a very big difference.