I've been given a rough estimate of 5 years for SH from someone within BA already, and as we currently have no ambitions for LH (we're both pilots, 2 young kids etc etc), suits me fine.
Things change fairly rapidly within BA. This year some will be getting commands one at a very junior level, but that is not indicative of anything. Last year the time to SH command was 15 years or so. What it will be next year or the year after is anyone's guess.
Many factors affect the time to command, some internal to BA some external. These factors are very hard to predict and are not necessarily consistent on a year by year basis.
TopBunk made some valid points regarding length of career and time to command. there are c 4000 pilots within BA, there are more FOs than captains as we use heavy FOs on LH.
SH rostering at the moment is changing and becoming more difficult. LH is likely to follow in the next year or so. Those that look to BA and think of BidLine are living in the past, BALPA has effectively allowed that to be destroyed. Consequently, this year there has been much jockeying for position, BA have also introduced new types while reducing old aircraft numbers.
All this has lead to a massive increase in the training burden, the old "truths" are changing, the jumbo is not the best fleet to be on, but a new best fleet is still a matter of opinion. Part time is becoming more desirable, some of the older pilots are now starting to retire earlier, rather than staying to 65.
Pension and tax laws are affecting the situation as will any global events like the global economic crash of 2008. No one know how the possible Grexit will affect the European economy. Life is uncertain and all that affects time to command.
I would take the estimate of 5 years with a pinch of salt. It could easily be right or massively wrong.
Work on 10 years for SH command and hope to be surprised, not disappointed.