How am I supposed to know what order to hit the generators for this riddle?

In Panessa Studios, there's a room with generators that holds one of Riddler's riddle.

To get the riddle, the generators needed to be hit in a particular order. As far as I know, there weren't any hints to the order that should have been taken. Detective mode didn't reveal anything. I couldn't see any obvious hints in the posters. After a number of random guesses, I was eventually able to get it.

Starting from the left: 1 5 7 3 2 4 8 6

How was I supposed to know in what order to hit the generators?

I believe it goes by the age of the person on the poster (starting at the youngest, from baby to grave, if you can consider "grave" an age haha).