Is it a red flag?

Should I be worried that he wants to get married/engaged at 18? We are 17 right now he is in no way controlling or abusive. We have been together for a year and so far so good? But i am reeeally not ready for that. It's not like i am planning for a breakup, i just don't believe in getting hitched at 18 right when its legal, you know? I did tell him about this and he felt a bit hurt (but he got the message). We finally agreed on possibly getting engaged if we make it to 22 together. Why do you think he wanted to do this so badly? (He just said he really wanted to make it official) He even suggested eloping behind my parents back at some point. Should I watch out? This is so out of character for him. Any advice would be really great.