My daughter [19F] accepted a proposal from her [19M] boyfriend of 6 months. Please advise.

Hello. I have a 19 year old daughter. She is currently working and living in NYC as a model. There, she met her current boyfriend, who is also 19. They have been dating for 6 months. He is not her first boyfriend, but it seems like the first one that she genuinely loves and cares for. I met the boy about 2 months ago, when he came and lived in our house for 1 week. He is a polite, respectful boy and I have nothing negative to say about him (but mostly because I don't really even know him).On the phone yesterday, my daughter told my family and I that her boyfriend proposed to her over dinner and that she has accepted. My wife and I, including her grandparents, were extremely shocked. This came out of nowhere. She has not discussed this issue with us at all, only with her older brother (who did not let us know beforehand either).We were happy for her but also very hesitant. She promised that the engagement will be a "long one", at least about a year. She also tells me that she is 100% in love with her boyfriend and that she is sure he is the one she wants to be with forever. I asked her about their thoughts on children. She seemed embarassed and told me that they wouldn't want to have kids until their late 20's. I asked her why not wait until then to get married. She then got a bit annoyed at me and brought up the fact that her mother and I got married when we were 22 after dating for 7 months, and that we turned out alright. This is a good point, but the situations are vastly different.My daughter has always been rather independent. She left home after graduating high school at the age of 17 to pursue her modeling career. She has enjoyed success in this field. For example, this year she already has earned more than my salary. If I must admit, it's not my ideal career choice for her, but her mother and I still are supportive of her. She rents her own apartment in NYC and travels a lot. She pays her own taxes and balances her budget wisely. She is a mature, grown up girl but that does not mean I think she is ready for marriage.I must admit that I am scared for her. She is so in love with this boy, and he with her, but I do not think they should get married. I don't want her to get divorced by the time she's 21. To me, she's still just a kid...I can't imagine her as a wife. It's unthinkable. Her mother is also unhappy about the idea, and swears that my daughter will regret it. She is also annoyed at my son for not telling us about his sister's plans for marriage beforehand.Please give me advice. I am excited, scared, and nervous for my daughter...I don't know what I can say or do at this point to make her change her mind. After all, she is an adult, we do not support her financially at all. What is there to do at this point?Thank you. via /r/Parenting http://ift.tt/2mc68sL