Marriage...NEED HELP

Sir my age is 18+ and my gf age is 19+...we don't want to marry now because of we marry it would be prohibited and denied legally...I know my gf from my 4th class...we want to complete our studied and want to marriage...but gf parents cought us and they stop education of girl...She don't have parents and she is staying with her grandparents...but she wants to stay with me,study with me and after I get 21 we want to marry.what is the solution....plz help me sir