I dont know how long it takes for them to reach full size but mine have doubled in size within 5 months from 1 1/2" to about 3" in diameter, im guessing they will be full grown within 18 months.
My two youngest have gone from about 1 in. long and 1 in. tall to about 4 inches long and 3.5 inches tall in 1 year. So I guess you could say they've quadrupled in size in a year from being babies.
My 2 older ones...one of which is my big boy!!!........now let's see here, I got them when they were about 3 inches long and 2.5 inches high and this was about 18 months ago....and now one is definitley 6 in. long by about 5 in. tall and the other is about 5 inches long by 4.5 inches tall......they have quite the different body shape that's for sure. So, they have almost doubled in size in the past year! I don't think they are the same Silver Dollar species..or family....or genus...or whatever it's called. But my 2 younger ones are the same
Seems like they quadruple in size the first year and then double again in the second
I would also like to add, don't know if this is correct, but mine seem to still be growing very slowly......my 2 older ones that is. So I don't know if they are in fact full grown in 18 months?? My 2 oldest are about 2 years old as of now.