As mentioned, all ages sail Alaska, and even Carnival's bulk of passengers are middle aged and above, no party ships yet in Alaska.
Key in planning is to look also what is OUTSIDE the ship, meaning, ports, time in ports, route (Seattle round trips do more outside passage sailings than my preferences allow
) , glacier - Glacier Bay is a highlight, and PRICE. Meaning you need to budget fully for costly excursions, you get only half a trip without them.
Any wildlife will require tours, you need to determine how much TIME you can allow and if you are considering an interior tour with a one way cruise?? Your group would benefit most with an independent touring of interior.
Shore excursions are port based, so look over any cruiseline shore excursion list for ideas. A lot can be booked independent, with the bonus of smaller groups and sometime s better tours, not always cost savings. Do your homework and make the right choices for you.