depends on the room and their diet - not just age.
we have a common that is about 10" whos 18 months old
If there is plenty of good food and plenty of tank space it can be as little as 8-10 months.
around 18 months for a common (12") and 2 years for a sailfin would be normal.
If food is not as abundant their groth rates will be slower (but not detrimental)