Morgan loves fetch, however, she grew up with a retriever, which I think has something to do with it. I also read the 5 months old thing, in GOLDEN RETRIEVERS FOR DUMMIES (hahaha) for the instance that your retriever did not already know how to retrieve, they said you have to teach them by five months old.
Even though she loves it, she will not play for hours like a retriever. She would prefer to bark orders at the retrievers as the play.
I also read that if you want to teach your dog to catch (treats or toys) that it must be done early as well, or else they are more apt to be fearful of things flying at their heads.