Century Plant

We have several century plants around our property, and of course, I've noticed some others around in various locations. This plant supposedly only blooms once in its life, sometime between the ages of 25 and 50 years old. What I find interesting is that all the large century plants I know of are all blooming this year. How do they know this is the year to bloom? What external signal are they acting on? All I know is that they all seem to be blooming this year -- and they are huge. I still have yet to shoot the ones around our house, but I did manage to take this photo of the one downtown San Diego, on 6th street, near Island. We walk past it every time we go to a ballgame at PetCo park. See how tall it is?