I'd probably be wary of an older guy dating my little sister but I admit wouldn't be able to do much about it. Usually 16-year-olds are jerks, but the OP doesn't seem to be one.
Anyways, what are his options?
1) Can't date older girls, a world between him and them.
2) Unlikely to date girls the same age as him, they're interested in guys 18+ years old.
3) Date a slightly younger girl.
I'd go for number 2 but that can be hard sometimes... Girls his age are easily impressed by older guys.
Besides if I'm giving advice I must think of ways the OP will satisfy his desire, which I presume will bring him happiness, regardless of opinion. He's just 16...