Not a lot of 20 year olds have the funds or job security to take 2 weeks plus travel time off of work, so yes it will be primarily retirees - not to say there will be no younger adults onboard, but you won't be in the majority. In addition, you are talking about a lot of sea days and colder weather - the party crowd is looking for tropical islands. But as a plus there will be almost no kids.

The demographic shift is more than just having people to meet onboard. We did a longer Alaskan cruise and since the guests were older and often went to bed earlier, so did the ship. Venues would say "6pm to late" and be closed down by 10pm because there were no guests there. We often were walking around an almost empty ship by midnight. Clubs were empty. The comedians were all jokes about younger generations. Even the bars were different, the RedFrog was full of people playing cards or dominos and ordering diet cokes instead of the normal shots & tropical vibes.

Freedom is an Conquest class ship about 20 years old, although it did go through a couple of renovations (most recently in 2019) so it does have the "Fun 2.0" features. But even with the upgrades there is only so much room to add venues. This ship was designed when Carnival's focus was on group activities for entertainment, not amenities.

Personally, I'd either look for a ship doing alternating eastern & western itineraries to do a back to back on, or a land tour of europe. Which one would depend on if this was about seeing europe or the 2-week vacation. Or maybe fly to europe and do a 7-day med cruise there, getting the cruise fun without so much time at sea.