Welcome to the site and the hobby. You have a lovely country to ride around in.
I've followed Dr. Ken Cooper Aerobics since the Army required me to build those skills 1968-83, and am now enjoying the benefits age 72. My knees creak decending stairs, my muscles are stiff & sore, but I can still get out & ride the bike into 10-30 mph wind (today from the grocery store). No electricity on bike now since it was 18 F 2 nights ago and will be 22 F Saturday night. Maybe battery can go back on bike in 2 weeks.
See bbcnews.com 11/25/13 "Never too late to exercise" review of an article in British Journal of Sports Medicine As always don't crash into a program or binge exercise. Gradual stretching of your routine builds capabilities painlessly. I try to get 30 minutes or more of panting 3 times a week, but I've been doing it for 55 years. My heart & lungs are proven capable. If the weather is too *****y to ride bike or push mower or something outdoors, I lift 3 to 5 lb weights & do some of the Army daily dozen in my den.