I was at my local bike dealer today talking about Trek Project One bikes. He was telling me one of the few he has sold was to a 75 yo rider. Said the gentleman's hand strength wasn't what it once was so he wanted to upgrade to Di2 shifting and hydraulic discs to make shifting and braking easier for him. I thought that was a neat story for someone taking advantage of the latest tech to keep riding.
My take, if you have that kind of money to drop on a Project One type bike and you want one why wait until it becomes a necessity? Might as well get it a little earlier in life so you can have more years to enjoy it.