Married at 18

So me and my boyfriend have been together for 3 years and both want to marry eachother and start a life together eventually, but it's been a rocky 3 years nonetheless. About a month ago he took me out on a date and it was really nice and he was a gentleman of course, and then he proposed. Like full on in the middle of the restaurant. And of course I said yes cause I do at some point want to marry him, but he wants to get married when I'm 18. Which is next year. His parents have been together since highschool so he's very optimistic about young marriage but I don't think the same way. Not to mention my parents hate him, and when I get married I want them there but I know if I told them that soon that they wouldn't support it. I try talking to him about it and he questions why I care so much about what other people think and I ask him what difference waiting another year till I'm 19 would make. We never come to an agreement on it and he said that every time I push it till I'm 19 or 20 he feels like I'm just going to inevitably keep pushing it off. Right now we have an agreement on the summer of 2018 which, little does he know is when I'm actually 19 but he's gonna figure it out eventually and I just can't seem to understand his perspective on what waiting another year will do.