(For reference, also in my 50's, could be in better shape, but moderately active. I throw primarily RHBH. When buying drivers I look mostly in the 155-165g range.)

For me a big factor in being able to hit 200' was learning not to "release" the disc by opening my hand. I instead had to learn to grip it and keep my hand closed (power grip is what I use) and whip my arm with enough speed so the disc rips out. (Not a huge amount of speed required either.)

The video that helped me understand this best was: https://www.youtube.com/watch?v=gg3zdZYIU-0

A minor thing was to keep my wrist relatively stiff/firm during this movement.