One thing that really helps me is keeping my knees warm. My rule of thumb is that if the temperature is less than 70F then I put on my leg warmers. Sometimes this feels a little goofy but I swear by it. Leg warmers are cheap and easy to take off later if it warms up. I’m now 67, been riding since college days. I’m not any great athlete but when I do 20-25 miles comfortably it feels great. Also stretching hamstrings is good, mine have always been tight. Best of luck.