I did 70 miles yesterday with about 8,000 feet of climbing, a good deal of well over 12%. I took one water bottle along. I refilled it once.
Let me tell you, don't ever try THAT. Although I feel OK today and I should be recovered completely by tomorrow's ride over the hills it nearly killed me yesterday.
I'll be turning 62 in another couple of weeks so I'm a bit early too. Of course I'll be doing the Foxy Fall metric next Sunday so I'll have to be easy on the old bod in the meantime.