Turning 69 next month. Some days are long days and some are short. Although I do enjoy longer rides it seems like the cutoff point for me has been about 50 miles. Mostly just due to the time involved. I'm not necessarily beat after a 50 miler but it just eats up the big portion of a day for me. I'm taking into account the prep in the morning, the ride and then a shower and lunch. I still love doing it though.