First things first. Regardless of how you release the ball, you need to have a fundamentally sound approach. Do you currently have a 4 step, 5 step or something else?
At age 50, the flexibility needed to throw a spinner or helicopter ball will be somewhat compromised. Without seeing what you look like when you bowl, I'm going to suspect to get any real RPM's from whichever release you use, you'll need to create a little snap at the very end. In the early stages, this will show up as a 'pull' but as you do it more often, hopefully you'll gain some control.
If a person throws a ball underhand allowing the ball to simple roll straight forward off their hand, they can expect a reasonable amount of predictability from that release.
Throwing a spinner/helicopter where the amount of rotation will initially be unpredictable will result in shots being sprayed over a wide area.
I would recommend you use the most relaxed grip you can and still hold on to the ball. What kind of grip do you have now? Conventional, semi, full fingertip or something else?
Do you have a video of yourself that you can share?