JayJay,

I think you might be taking this a bit more literally than necessary. At those distances, adding a mile or two wouldn't hurt. For example, if your very first ride happened to be 20 miles, you would be adding significantly more each week. And, the numbers are for each ride, not over a week. You'll want to ride as often a week as you can. I hike too, but they are really two different types of exercise. Hiking is a slow movement, and your cycling should be at a high cadence.

The 10% is a general guideline, but usually when you're already at a higher distance. Just start riding as often as you can, as many days a week as you can. (But don't cut out the hiking -- that's a great weight-bearing exercise, good for your bones!)

Don't let your age define you. I'm riding more at your age than I ever did when I was younger!

Edit: I just figured out your personal format plan. No need to do those shorter rides. Keep going with the longer rides. If you get really intense in your training, take a 'recovery' week every 4 weeks, where you don't push as hard.