First of all, at age 19 this girl is still VERY MUCH a child. Her brain isn't even fully formed either. The age difference is going to be a big deal in that this young girl will be doing a lot of growing and maturing the next ten years of her life. Sure, you may love her, take care of her etc., but it's very probable as she matures she will grow out of you. At this point all you will be is a male influence on her, yet she is still going to be growing and maturing a lot and is far from your mature equal as in many ways she is still a child yet. Also, she should be thinking about what she wants to be in her life, and be going off to college. And she should be educated so she can be independent and take care of herself. If something were to happen to you, it would not be fair to her not to be able to take care of herself, or the children if she has them.

Also, having a father can be a disadvantage too in that some fathers are VERY poor examples of the right kind of man to marry and have a life with.

If she was already 30 and you were 50, it would still be a bit of an age difference, yet she would at that age be way more mature if she had an education and time working and learning and developing herself.