You can have a good talk with your girlfriend, clearly express your commitment and hope to her, and your willingness to build a life. I believe she will understand, and then convince her parents that you can choose the way of getting engaged first and getting married one or two years later.

Of course, it's not that you can't get married right away, but you are still young and don't have to worry about having children. It can be accumulated for several years. In fact, marriage will not bring great economic pressure. You may be a little worried about this. In fact, we have to build a life together anyway. Two people are sometimes better than one person.