Commands are a function of two things: retirements and expansion. Virgin has relatively few retirements as most captains are in their 40s, but is expanding at about 10% per year. At the moment, that means command in 7/8 years, though there is no guarantee that this figure will remain valid. If expansion stopped tomorrow, command would go out to 15 years or more.
It's been pointed out to me that this doesn't accurately convey a full enough picture. The 10% expansion I referred to is in
capacity not in
aircraft. Hence, the numbers of aircraft (and thus commands) will not increase as quickly as the number of seat-kilometres available. Logic suggests that time to command will increase when the airline reduces its expansion rate, which is unlikely to be maintained indefinitely in the mature longhaul market. Thus a new-joiner now may need to be thinking in terms of 10 years or so for command.
Hope this helps!