~*~changing My Last Name~*~

I don't know what to do. I care for him a lot and I would love to be his wife but Im only 15 years old. should I say yes and take his last name like I want to? should I say no and risk losing him forever? I might say no but only because I want to wait till senior year. he's the love of my life and I hope he can understand me. I want to marry him but he has to understand that the only way I can marry him is if my mom signs and I know for damn sure that she's not going to sign the papers with me only being 16 maybe 17 or 18 but not 16. baby, if you're reading this don't take it the wrong way I'm not saying I don't want to marry you I just want to wait till senior year.