Good luck xBook an appointment with your vet for a lameness work up and see what they say about a bute trial or steroid injection depending where the source of arthritis is. Arthritic horses are better in low level exercise and lots of turnout providing they can be ridden pain free. I don't see why you couldn't ride your horse again providing a) your vet agrees b) the horse is pain free c) you keep sessions shorter and avoid certain surfaces that may aggravate your horses problems d) you come up with a sensible rehab programme. This might entail different shoeing and a different way of riding. Its better to ride shorter sessions regularly rather than 1 hour once a week if that makes sense.
My mare's nearly 23, has arthritis, has been treated by the vet for it, is on a sachet of bute everyday and is kept in work by hacking, usually 3-4 times a week in the winter but six days in the summer. Occasionally I will have a trot and canter for a couple of minutes in the school following a hack and I go on fun rides in the summer, I watch the surface and she is remedially shod. Recently my physio did a session with her and said she was pleased and couldn't find anything of note wrong with her at all which was good. She always has her ears forward on hacks, clearly enjoys them and is a pleasure to ride.
Only you and your vet know your horse, its history and whether this is a realistic goal or not. Your horse certainly isn't 'poor' and might be glad of a change of scenery and 'dragged back into work' again.