I recommend Royal Carribean because they have a great Inside Passage cruise - Sawyer Glacier I think is the title. Leaves from and returns to Seattle - 7 days. You'll have a mix of age groups but should be plenty of 20 somethings. They have a zillion excursions. There are several kayaking - in the Tracey Arm Fjord - you'll be surrounded by glaciers! If you go May, early June - bring warm clothes. If you go mid to late summer, bring a lot of mosquito repellant!