Computer: Imac Late 2009 - 12 gb Ram - SSD for Catalogue _ Intern HD for pictures. Mac OS 10.9.5
Lightroom : CC, last version.
I have a Late 2009 iMac also and same crashing issue. Turned off the Graphics Acceleration option and no crashes.
You both have six year old Macs. I wouldn't expect benefit from the GPU and turning off acceleration is recommended for stability.