GM
I think, notwithstanding hours, knowledge and ability there is a right time to get a command.
You need to be of a certain minimum age commensurate with maturity to give authority and confidence to your crew, handling partners and passengers. So depending on the individual and aircraft type earliest age would be late 20's to early 30's. Time to learn the aircraft and job properly can be, say, 5-10 years so after that time you're ready and hungry for the command. Unless you're constantly being challenged with new routes or fleets you can become stagnant in the RH and fall into a 'FO mentallity' with not thinking about the wider issues of the job.
If you join an airline in your 30's with a 15-20 yr wait for a command slot you'll most likely be 50+ before you get the chance at an upgrade. It's a know fact that changing/learning is more difficult at that age. Combine that with the fact you have been in the RH seat for a long time it becomes an uphill slog.
Most people aspire to a command. If you don't and are happy with your lot as a 'professional' FO there's not a problem with whoever you work for.