I would be guessing. The landscaper (second owner) that I (third owner) bought my home from had it installed in the back yard, relocating it from the front where it was getting too large for the spot it was in. So that leads me to believe it was installed back in the day when it was very small and no care was taken to see into the future that it would outgrow its spot. And the home was built in 93 / 94, and probably initially landscaped shortly thereafter. So lets assume the plant was a couple years old at that time when it was first planted out (they probably didn't plant out seeds, right)... it could be ten or fifteen years old by now.
You cannot see the main stem in that photo as it is blocked by some fronds, but it's up there, prob 7 or 8 ft where the crown begins.
Even if I asked the guy I got it from, he wouldnt know as he bought it and resold it to me only a few months later. I could do some research as I have the # of the builder / first owner, he might know more...
But this should be a good round estimate, no?