My father is about 10 years older than my mother. That means that my mother wasn't even born when my father was in 5th Grade!
In other words, simply because a person is somewhat younger than you doesn't mean that love between the two isn't possible. Of course, I'm not saying that adults should be dating 8 year olds, but the possibility of marrying them when they're older is certainly possible!
But acting as an older brother to a girl is super cute and you should totes do that Raymondbl.