Hey @David_G 
Welcome back to training 
It sounds like you are naturally gifted in sports, and the fact that you’ve had such an extensive history should make your comeback easier. 
As you mentioned, our bodies are amazing at keeping muscle memory. I’ve personally stopped racing several times in my career and every time I came back (even after pregnancy, which let me tell you destroys you on so many levels) I dove head into a training plan, and it was the best thing! I personally always preferred structure training because you can measure improvement better over time and to be honest it will get you to those century rides faster 
As @JoeX mentioned you could just dive into Plan Builder and create TR plan. I would just consider going with a Low Volume plan, or even a Low Volume Master’s plan (2 intervals and 1 endurance per week), and over time you can see about changing to a Mid/High Volume.
Alternatively, if you just want to ride your bike for a while and settle back into the feel of riding and all, as @AJS914 mentioned, you could use the TrainNow feature to recommend workouts on the days you’d like to do TR Workouts. 
It’s been a while since you trained with us; we’ve developed really cool features in the past few years like Adaptive Training, AI FTP Detection and as of recent Red Light Green Light which monitors your training to prevent long term fatigue, which becomes key when getting back into the flow of things. I know I can get carried away after a long time off 
We also have a great Customer Support Team and offer onboarding calls, so we’re more than happy to get into a Zoom call to get things dialed and answer any questions you may have!
P.S.: I’ll send you a DM about your old username with us to see if we can find it!