Return to Capru. At this point Capru asks you to 'Return later.' His concept of 'later' is about 2-3 game weeks (exactly 24 hours real time). When he is ready a quest feather will appear over his head.
Use the Gryphon Call to summon your pet. Then left-click your Gryphon pet and choose one of the following options for a quest to 'grow' your gryphon (you may complete the quests in any order, but only one can be completed every 18 hours):