Malasiacadet,
Speaking for EK.
VERY hard to tell as it depends on the future expansion of the Airline.
It would take about 5 years to get the required expeience (6000tt, 4000 "Hard Time" 3000 on EK type) so it would then depend on whether the Airline is expecting to expand as much as it is now in 5 years time.
SO- could be 5 years, could be 10.