Regardless of age, if a well conditioned athlete's sleep and diet are on point, training twice a day shouldn't be that big of a deal. Not like it is news, but sleep and diet are as powerful tools for performance and recovery as anything.
I think masters age athletes should train as much as anyone. Perhaps they should be mindful of volume and intensity but the more you keep moving the better off you are.
At 48, I tend to seize up and feel crappy if I take too many days off.