My younger sister is 17 and she is dating a guy that is 24. At first I felt pretty uncomfortable with the age difference (as did the rest of my family) even though my sister is known for being very mature for her age. It also didn't help that my boyfriend is younger than hers, and I'm four years older (I'm 21, he is 23).
However, after actually seeing them together I actually defend their age difference to everyone else. My sister and her boyfriend are probably 1 or 2 years apart in terms of their mental age.
Although I think it really is a case by case thing (as many people have said here
), it does get difficult trying to convince other people that the 7 year difference is not that big of a deal