We cruise on Anthem every January for 11 or 12 nights. You will find the crowd to be older experienced cruisers. We see the same cruisers every year. Sea plex is rarely crowded. It is a very relaxed cruise. There may be a crowd for the shopping talk etc. belly flop etc.
the seas of course are variable. We have left in a snow squall and in nearly 50 degrees. Some rough. And some smooth. We have celebrated super bowls etc on board. We are booked again for next January. And barring a surge in Covid 19 we will be there. Go for it ! The ship is amazing. The indoor pools are great.