Relationship advice?

Hi so I’ve been in a relationship with my boyfriend for four years. But I’ve known him ever since the 1st grade lol but he’s a marine. He just got back from a deployment from japan and now he’s currently in San Diego. We’ve been in a long distance. But we do see each other as much as we can. He surprised me from japan and came to our hometown and proposed. So we’re engaged but still in a long distance for now. We’re both 21 years old and I go to school while he’s in the military and starting school. But the point is that I will be moving to San Diego so we can be together but also he wants to start a family. I’m all for the idea but I’m just scared of what others will think because we’re so young.