That was me paddling left, hate to disappoint you but, I'm your age, surf as much as you maybe less,( that was my first surf in almost 3 months)..due to work and I live 50ks to the closet beach or 3 hours to surf with my mates, had a major shoulder recon a few years ago and the other shoulder needs one now.
Don't stress, just go to the gym, speak to a Personal trainer and let them know why you are training and for what sport, go for a swim or just try and get in the water.
Worst case get one of those 'Chuck Norris' training machines, not the cheap one but a middle of the road and some of the exercises are the closest thing to paddling.
go for it old man

Bumps