I have a bf,and he's the first,now his asking me......?

well he is my first boy friend,we've been together for 4 years,now i'm 20 years old,and he's 24,now he's asking if i want to merry him,what should i do?should i tell him, no and breake up with him bec.i want to enjoy my life,them get merried or accept his proposal?but we always fight.what should i do?