My ride is 7.5 miles each way. I ride from the East end (upper beaches for those that know) down to south Chinatown in Toronto. Takes me about 30 mins in, 45mins-1hr back home - the ride home going back up the hills that I come down in the morning.
I only ride in a max. of 3 times a week so far, the uphill and against-the-wind factors (particularly riding across the lakeshore) really seem to bog me down in terms of my muscle recovery / tiredness levels, etc.
I maintain (according to my tripcomputer) an average of anything from 12-15mph, I don't go all out but those big hills that I used to be discouraged by don't seem nearly as bad now after a few weeks of riding in. My actual 'cruise' speeds are more like 16-20mph, typically hovering around 18 though.
I'm 25 and working to get/stay in at least some 'reasonable' shape. I sweat like a person who sweats a lot, so I found a local-to-work gym with reasonable membership rates that I was able to use for my showering, as it's absolutely necessary for me and my overactive glands..
What I find myself doing on the trip home is taking an extra 20-30 mins to stop off here and there and admire some of the lesser-known/seen parks or little alcoves near the lake just to relax by, I love this part of my day and look forward to it each time I ride in.