Any relationship can work if your willing to work hard at it. What I want to know is why is a 17 years old with someone who's 19. What is the purpose of the relationship? Why is there a relationship in the first place? When I often see that wither it is the girl who is younger then the guy or the other way around, it often comes down to the parents. Are they in agreement to this relationship? And why? In my opinion I don't find it appropriate for a person over 18 dating someone below 18, unless they are turning 18 very soon. Sometimes the older the person is, the high chance they can take advantage of you if you don't know any better. I've often heard these things happen even if it is just two years apart. It's the line between being over 18 or under that is often the case.
For a while, sure. To be honest, girls usually mature quicker than guys, so a younger guy with an older girl might not be the best thing. Depends on the guy, though. If his maturity level is on par with her's, then why not. I konw speaking for myself, I matured by leaps and bounds between ages 17-19, so for me a 19 year old girl probably wouldn't have hooked up with me outside of sex when I was 17.