Hi Dave & welcome to the forums. Your fifties isn't old. You have a decade plus yet until you start to hit multiple privileges of that real physical age barrier.

A guitarist first and keyboard novitiate second, here's my take. Someone experienced with keyboard prior to coming to guitar may offer you their greater experience of their journey, but here's what I didcovered as a post-novitiate cum intermediate guitarist taking up keyboard a couple of years after guitar.  Your years of keyboard will be extremel;y useful as the same theory applies. Keyboard is considered -and I found it so, easier to learn initially because it's linear, and so very useful for grasping concepts literally in black and white.

Unfortunately the guitar neck isn't that friendly, and the fingers learning it is largely down to greater applied repetition until rote.  With all that motility from playing keyboard too, you should find the transition to guitar and your journey easier than a complete neophyte.  Have fun with it. That's the prime objective. 

Cheers!