Here’s a question for ya: Is it necessary or desirable to do back-to-back training days if you are training for a one-day event?
I’m asking for myself, obviously, but also for someone I’m trying to help get ready for the Etape du Tour. In the past I’ve nearly always done multiple days of training in my program, but this year I’ve planned it so that I’m usually doing a lot of volume each day and then have time to recover before the next ride day. To me this makes sense as long as the volume and necessary intensity is in the program, i.e. the training mimics the event, more or less.
I guess what I’d like to know is if there is a specific physiological benefit (for a one day event) by doing two or more days in a row?
Teach me!
The Vicious Cycle 
From Coach Rob:
I’m sure there’s loads of sports science out there and the answer to the question will vary depending on who you ask. Having raced 7 Ironman triathlons, I may have a perspective that is transferrable to your event.
It’s highly unlikely that an athlete training for an ultra will do the full distance prior to the actual race. If they did, they would be risking injury, or athletic fatigue syndrome. So the question is how can you train your body to experience the stress you’re going experience during the actual event if you don’t do the full distance in your training. This is where doing back-to-back long workouts can simulate the physical and mental stresses associated with your ultra, because the second or third days start with a fatigued body and a mental state that questions your sanity.
When I prepared for the Ironman, I never did the whole distance in training, but we would do back to back long hard training sessions so we started the second or third day in a fatigued state. This allowed us to experience how we might feel in the actual race while avoiding the risk of injury and prolonged recover times.
So in my completely unprofessional opinion, which is based solely on first hand experience, I would suggest doing back to back long training sessions are quite beneficial. That said, be very mindful of your recovery after such a multi-day brick, especially given your age. Sorry, this too is a reality you have to consider.