I've been riding for a little less than 4 years now. I'm 59. I will be riding from San Francisco to Los Angeles in June -- for the second time -- to benefit AIDS research and education. Here is the simple training schedule they give us. At the end, you should be able to ride 60 - 100 miles a day over 7 days. It worked for me.
Month miles/wk Longest ride Days per week Total trng hrs/w
Oct 10 -15 5 - 10 1-2 2-3
Nov 15 -25 10-15 1-2 3-4
Dec 25-50 15-20 2-3 4-6
Jan 50-75 20-25 3-4 6-8
Feb 75-100 25-40 3-4 8-10
Mar 100-125 45-55 4-5 10-12
Apr 125-150 55-75 4-5 12-14
May 125-175 75-90 5 14-16
You're already well on your way.