Mentioned this in the past:
If you join BA tomorrow, you will not get a command for a very long time. Hand Solo is probably about right. Since the new pay deal, a SH command occurs at LGW at a seniority number of approximately 1800, SH LHR at 1400, LH LHR at 1000 (ish). If you join tomorrow, you seniority number will be 3100 ish. As the large retirement bubble ends (plus the advent of new legislation in 2006), your seniority number will not change by very much (probably around 50 places per year). You do the the maths.
Keep in mind that there are a lot of senior guys aged around 30. For example, I flew with a 777 skipper the other week who was 36. He will be a long haul captain for 19 to 26 years, depending on when he retires. Bear in mind, he joined at 19 or thereabouts so it's taken him 17 years. Talk about "right place at the right time".
DEPs will almost certainly join on the A320 or the 777. There is enough demand from within to fly the -400.