It may have been moved here from another forum.
As for the original question, there are amny factors which determine rank. Some airlines will only have F/Os and Captains. Some may split the co-pilot's rank into various levels reflecting on their experience, or more usually time in the company. As for upgrading to the left seat, seniority is the usual factor With the better employers, people won't leave and time to command may be in excess of ten years or more. But time to command can be very short in an airline with a lot of throughput or which is expanding rapidly. Plus, a minimum experience level is set and this is never usually less that 3000 hours for narrowbodies and 5000 for widebodies which are levels set by most insurers.
My company has Second officers (one stipe), Junior First Officers (two stripes) and First Officers (three stripes) as co-pilots. The criteria for promotion and better pay is time. But our sister company which operates a lot of long haul routes reserves the rank of SO for the cruise pilots. They only become a JFO on upgrade to the right hand seat proper and a full rating on the aircraft. They also subdivide the FO rank into those who are cruise command qualified and those which aren't. The latter weat 2 and a 1/2 stripes.