I just got back from that very cruise and didn't notice any over abundance of people from Puerto Rico. We usually stay in PR
for several days after our cruise too, since we really enjoy PR
and find the people to be very friendly. You will find a very diverse mix of people on the Destiny. I would say most are between the ages of 20-50, median ages.
Usually the prices of the cruise lowers during hurricane months in the Summer and usually that's when the Puerto Ricans tend to travel most on the ship. I wouldn't worry. Mix, mingle & be merry!