The last three years I participated in a fundraising bike ride (for BORP) in Sonoma County (CA) riding a 17 year old Specialized Hardrock. First two years the 25 mile was comfy; last time I did the 100k (which was actually 64.5 miles)..included some challenging hills. I'm 64, in good shape, and although a newer, lighter bike is soon in my future for this year's ride, I think stamina & strength is the key. You'll do great!