I did the Solvang Century here in CA last Saturday, and completely ran out of steam around mile 85. Literally had to rest every 1 1/2 miles, and finally gave up and sagged to the finish. Only my 2d dnf out of 6 centuries, but it rankles.
There's certainly a training issue to be addressed: I need more miles (hard to do and work too) and more hills. But I suspect a nutrition issue also. Normally I don't eat much breakfast, and snack through the day until dinner. I pretty much do the same on Century days: very light breakfast, and I take along power bars, gels, etc. I snacked pretty aggressively at every other rest stop. The hills were steep and the headwinds ferocious, but the temperatures were perfect, and I still couldn't keep my energy up.
Any and all advice welcome. BTW, I'm 6'2", 190 lbs. And I'm 69 years of age. But I refuse to excuse myself because of age.