As a Clyde and over 50 I have been doing about 70 rpm's. My legs weigh about 50 lbs each and i find much faster and it seems to be wasting energy just to move my legs. My ability to keep a fluid leg motion suffers above 80 rpm's. I average 10 mph on most rides but i am still tweaking the bike fit on all my bikes for improved comfort. I like to ride a minimum of 30 miles at a time. That is about 1,000 calories for me. I can get my exercise without overdoing it.
As i get more comfortable on the bike I expect to gain a few rpm's . 50 rpm's on a hill in low gear suits me with a 28/28 gear and 70 rpm's on my hybrid or touring with a 28/32