Sturgeons grow actually very fast, in some species you can actually see massive growth rates, which are perhaps only surpased by arapaimas. And coelacanths (which you won´t never have in an aquarium) grow also not that slow.
Yes many places will quote slow growth rates for stugeon, species like female beluga will hit 2-3" per month while even the acipenser ruthenus which has the slowest growth of all sturgeons i've kept grew at around 1" per 2 month