How Do You Know?

I neighbor's kid (early 20's) came over and said he'd noticed we have apple trees.  He said they have apple trees, too, but don't have a clue when to pick them.  I said to notice when they look good to him, pull one, eat it.  If he likes them like that, pull more.  Different apple trees have apples that ripen at different times so it is hard to tell somebody else when their trees will have ripe apples.