The BMB randonee blogs are great to read. I could never keep up the pace and doing it on a fixie is super-human IMHO. In fact going ultralight without a tent etc and trying to average over 100 miles per day turns touring into back to back randonees. For 5 days I averaged 90 miles a day from Ontario, along the Erie Canal and back to MA on a fully geared bike with about 20 lbs of gear and it started to get to me. But I'm over 50 so things begin to ache and I'm no where near the fitness level required for BMB, LEL or PBP.
The woman I mentioned is amazing and one of my cycling heroes (outside Machka, of course). She is a highly accomplished symphony musician and apart from anything else, has a wonderful zest for life. Maybe their is a correlation factor with riding fixed gear
As to age, forget it. The average age of randonneurs is quite high, and in fact could be regarded as a "mature age" sport. Maybe it's because the older riders have more time after taking care of family, and maybe they are better financially equipped. But 50 is about the average age for PBP, if I remember correctly.
Stories abound, of course, about people who set out to do the PBP, LEL and other 1200s without having ridden much before. I think LWaB has talked about a woman who rode PBP by only doing the qualifying series, and then the 1200 itself.
Like you have done with ultra-lightweight touring, much depends on your levels of organising ability, and experience (given what I have just stated above).
I'm 60. My first PBP (or any 1200 for that matter) was in 2003. I had a DNF in PBP in 2007 when I was riding a fixie (but the fixie wasn't the cause of the retirement), and then life things got in the way. But Machka and I are gearing up to get back into LD again. If I can do it, you sure can!
Sorry for the drift in topic, but the fixie was mentioned!