Depends on a great deal of factors. Just a few;
1. Age you started flying.
2. Age when you got your first job as an S/O or F/O.
3. How many hours you had when you got your first job.
4. How many hours you fly per year.
5. Minimum number of hours required by your company to be considered for command.
6. Number of commands available in your airline over time. (In a seniority based system it is even more relevant).
7. Airline expansion or contraction due to market forces.
8. Whether you take the command in one of your first airlines or move on to a better job before becoming a captain.
9. Willingness to 'go anywhere' or not to get the command.
10. World events.
And I am sure there are many more besides. In my case, I started flying in 1997 at the age of 30, first airline F/O position at 34 and am just about to get my first command (airline as opposed to single crew ops) at the age of 37. Not overly fast, but remember 9/11 was tucked in the middle of all that. Having said that, time to command in my company was 15 years as little as 12 months ago....... unfortunate for those who joined 15 years ago as they have just got their commands and I have only been there 2 years with a good chance of it due to fleet expansion and willingness to go wherever.
PP