"Training" is complicated. How best to do it? There are many different paths to success. One way to start is to join a once-a-week group ride where the riders are a bit faster than you are. Watch how they ride, where they go moderate and where they go hard. Try to stay with them. You'll probably fail, so simply keep trying with that group. Make sure you know the proposed route so you can finish the whole ride when you get dropped. You'll gradually get faster. The rest of the week, ride moderate as much as you can. You want about 100 miles or so per week, year 'round (or the equivalent hours at a similar level of effort). You should work that up to 150 miles in summer. Let that be your training. Use TrainingPeaks or some other software to record and analyze your rides so you have some data to see what you're doing, like how much time in what zones.

Anyway, that's how I started training 25 years ago. I took my resting and standing resting HRs every day to make sure I wasn't overdoing it. That's important. Gradually, I developed a training routine simply by trying to do what had worked, like 45' of Z4 and 5' of Z5 on that group ride most weeks, but not every week. Big things to learn are how best to fuel and hydrate on long and hard group rides. 3-4 hour group rides seemed to work best, with a few longer rides here and there. I found doing strenuous weight work at the gym for an hour twice a week to be necessary at your age to build up the muscular endurance that it takes to ride that hard, that long. Start light with high reps and gradually increase weight and reduce reps. Friel's classic guide has lots of good information about this and everything else. Study it: https://www.amazon.com/Cyclists-Trai.../dp/1937715825