In general, it would take them a few years to get to that size... maybe 3-5yrs at least It also depends on the hobbyist. Some Koi don't even reach that size due to poor caring with regards to poor water quality, over crowding etc. Filtration and water volume per fish is very critical.
What we also have to remember is, Males don't grow as big. They could be blessed with good coloration, form and and pattern but they are not used for shows etc. They are just for breeding It's the females that always get all the credit!