My big old Agave salmiana ssp crassispina (syn. Agave coarctata) is making its bud, ready to bolt upwards in spring. I reckon it is 27 or 28 years old. Exciting and sad at the same time.
They die afterwards so, yes, it is a rare, one-off event for the agave concerned. :D
But in terms of agaves flowering generally, historically there were only Agave americana plus the odd salmiana that have been grown in milder coastal areas and, generally, they only flower ofter 20-30 years so it has always been a rarity. But the last 20 years or so has seen a massive expansion in the range of species and locations of people growing them so, increasingly, we will see them flowering. The first montana, gentryi and even ovatifolia are starting to reach flowering size now.
I'm hoping this one will set good seed as it is not that common in cultivation yet one of the best to grow. Might even get the step ladders and paint brush out :)
Some of the Agave americana planted out in public spaces in Falmouth have flowered in recent years making a very impressive sight so, yes, pictures please.
It is a pity that the Falmouth gardening staff don't remove the dead and dying plants after flowering until they become a mound of mush which can take another couple of years, they do look a mess.