Many years in security - engineering through leadership. The comments here are quite solid. I'd add that CISSP requires documented security experience + a CISSP

Many years in security - engineering through leadership. The comments here are quite solid. I'd add that CISSP requires documented security experience + a CISSP sponsor to sign off. I started from a C.S. background, but you can start in many routes: if you have CS background, find a small security services company and apply. You might also do a 1 pivot move, where you use your mech/research background and combine it with security to become a specialist in that area (IoT related may be easiest pivot). Also, check out cybrary.it for significant free learning resources. Too exhausted to add more - but other commenters have great ideas.