Was just on Symphony last week:
Demographic - For a cruise sailing a week before school restarts, there were very very few children and teens. But i didn’t find the cruise average age to be high. A lot of late 30s - late 50s, mostly couples or small groups friends/family
capacity - symphony holds around 6500 guest on a full load. We sailed at 1800 guest. Originally capped booking number for that ship was 40% capacity, but a little more than 10% canceled/moved their sailing last minute due to delta variant fear. It was a little spooky at times, and the casino energy (fully vaccinated area) wasn’t exciting, but there was never a line or jam for anything. To put it in perspective for those of us who have cruised before, you could make your way to the pool deck at 11 am and still find ample chairs (and they have distanced and reduced seating)