For example, Stephen Davis is 26 this year, but it's possible that his body thinks he's more like 24 because he hasn't taken nearly as many hits in his NFL career as most backs have by the time they're 26. That's not an unreasonable assertion. The trend here is not quite as clear in terms of finding the peak, but note the cliff at age 30. Let's try slicing it this way. This is a much different picture than what we saw for running backs.
Young receivers are more likely to improve than young RBs.
My guess is that this occurs because young RBs are more likely to already be good than young receivers are. Old receivers are more likely to decline than old RBs. I can't think of a good explanation for this, but the data is compelling. Something to think about for you dynasty league types. Quarterbacks I expected to find no clear trends at all for QBs.