You rise to the occasion. From my experience, limited to a few years as a loco f/o and a few more as a flag carrier ditto, and a little bit of work with flight safety. Having flown with captains ranging from brand new 25 years olds up to 60+ guys with 40 years of experience, it's very rarely the young ones that are the problem. Most of the bad CRM I've seen comes from the older Captains and f/os. The truly brilliant ones is a vast mix of age and experience. My conclusion is that personality is what counts - not how long time you've been incompetent.