One of the worst, most depressing experiences I have ever had on a bike, or for that matter off a bike, was hitting the wall on my first day climbing in the Colorado Rockies. The day started with 30 miles from Pueblo to Wetmore. In the process I climbed about 1,400 feet. It was a bit challenging but not too bad.
Between Wetmore and Westcliffe, however, was a 3,000 foot climb over what I learned today is something called Hardscrabble Pass. The Google says the distance is 15 miles but other accounts have it at 12 miles. Either way it is a relentless grade of between 6 and 8 percent for most of the way up.
Today I read an account of a bike tourist who did this ride in 2009. He describes having to stop every 1/10 of a mile to avoid going anaerobic. His legs kept tying up as he rode. With no experience at this sort of thing, I didn’t stop until I was completely unable to get a breath. At around 7,500 feet, I leaned over my bike gasping. (My asthma didn’t help a whole lot.)
Another rider broke the Pueblo to Westcliffe ride into two days. He referred to the pass as “the wall.” He took five hours to ride 15 miles over the top. And he walked three times.
After starting and stopping several times, I ended up walking the steepest part about half way between Wetmore and the pass. I felt humiliated, but these two journals assure me that my failure to ride nonstop over the pass had nothing to do with my fitness or age.
My ego feels better now.
A Few Spokes Shy of a Wheel 
I thing all of us bloggers have hit at least one wall on a bike ride. Those that have never hit a wall riding have sponsors.
It helps knowing others struggled the same struggle. Regardless, this is a great accomplishment.
Glad you could find some evidence to retro actively forgive yourself for walking. And btw stopping because you can no longer breathe is a totally legit excuse. 7% for 12 miles sounds brutal and I live in a very hilly neighborhood so hills are no stranger to my rides but doing my favorite local road climb x 12 doesn’t at all fun.