No more than 72hrs. One week is too long.
I am days away from being 67 years old. Would you agree that the older one is the longer it takes to recover? I've been told this is the case, but I suspect it varies by person and how hard they workout.
My workouts are still pretty intense despite being an old codger. I work out not less than one hour and often as long at 90 minutes per workout. My routine goes pretty much like this: Monday I work arms, Tuesday hamstrings and calves, Wednesday back, Thursday it is delts traps and abs, Friday chest and finally on Saturday it is quads and calves. I limit my rest time between sets to two minutes or less and about the same amount of time between exercises. If someone is using the equipment I need, I move on to another exercise rather than wait for it. Although I am friendly, I keep talk to a minimum. As many days as possible I finish off by doing 20 to 30 minutes of cardio.
One advantage I found with waiting a week to repeat working a muscle group is that the muscles react as if each week is something new for them....gaining the advantage of shocking them each time I work them out. Plus, I don't get bored with my routine as easily as I did when I did the normal twice a week split.
I am just finishing up a two month holiday from the gym. I'll likely start back with the same routine I was doing in June, but I am always up for new ideas too.