Allowing for fails a committed student with no exemptions can qualify in 6-7 years. It can be done in 4 if most exams are passed first time. Something like the below allows for a generous amount of fails and assumes they take the smaller exams CA2, CA3, CT9 alongside the main exams
CTs in 5 sittings or 2.5 years
CA1 in 2 sittings or 1 year
STs in 4 sittings or 2 years
SA in 2 sittings or 1 year
With exemptions it can be done much sooner, if you come out of university with your CTs, and pass CA1 in your first year you only have 3 exams (ignoring CA2, CA3 which don't require as many hours studying) left to qualification at the age of 22 or 23, that's an extra motivation in itself knowing you are close to finish line.