A recent undocumented change has adjusted the level requirements to use the portals to Valdrakken in capital cities — characters must now be level 70 for a quick trip to the Dragon Isles.
Players looking to bring a leveling character or alt back to Valdrakken will find that they have to take a much longer trip, either via the Defiant Dragonscale zeppelin from Orgrimmar or the Rugged Dragonscale ship from Stormwind.
While we're unsure exactly when this change took effect, it was recent — not long ago, characters above level 60 were able to come and go freely via the portals as needed.
Characters below level 60 have consistently had trouble with the portals from both sides, and historically needed a summon or mage portal to reach the Dragon Isles, but this now proves a nuisance for characters not yet at max level.
For those still leveling, there is some solace: simply set your Hearthstone to an Inn in the Dragon Isles such as The Roasted Ram, and you'll be fine. For those who enjoyed leaving their Hearthstone location in other areas, however, be prepared to wait for your ride to arrive.