If your main problem is pain, and you can raise your arm above shoulder level, then you may be a cadidate for a hemiarthroplasty with an extended articular surface. See this link:
http://www.rearmyourself.com/article...%20arthropathy
This option avoids the potential downsides of instability following Reverse shoulder---and can be revised down the road should function decline. I would also suggest checking a nerve study to ensure that suprascapular nerve dysfucntion is not contributing to your pain, in which case an arthroscopic release of the transverse scapular ligament is an option. In addition, tenotomizing the long head of the biceps may also result in pain relief.
However, if your function is such that you can no longer elevate your arm, and you have disabling pain, then a Reverse is an option even at your age. Designs are constantly improving---and so it is not a given that your replacement will fail with time.
I have attached 2 x-ray pics below--one of a standard stemmed hemiarthroplasty with an Extended articular surface (which articulates both with the glenoid and the undersurface of the acromion) and one with a cap.