Given your age and current fitness level, I think just riding as much as you can is your best bet.

If you've got a smart trainer, try Zwift. I don't use it, but people who do seem to like it. (I prefer to just watch TV when I do my trainer workouts.) There are group rides you can join to help push you to ride harder.

I believe Zwift, Sufferfest and TrainerRoad all offer canned training plans designed to help people at different points in their riding development. You might want to check some of those out.

Lastly, if you really want accountability, find a coach. (PM me if you have questions on how to find one.)