I dont have kids, but in todays world, none of this should be surprising. Not taking a shot at you or anything, just saying that compared to other things that go on, this is relationship is probably on the mild end of things.
Then again, some people could look at this and say that 4yrs isnt that big of a deal.
Surprising, no; appalling, yes. And I'm not taking a shot at you, either, but GOOD parents don't allow 11 year olds to date. And the 4 years between 11 and 15 are definitely a big deal. Look at it this way: an 11 year old is in elementary school. A 15 year old is a sophomore in high school. It's NOT the same as a 24 year old dating a 28 year old.