Dwalin the Dwarf

[Thinlómien]

Originally Posted by William Cloud Hickli

Tolkien covered the lifespan of Dwarves in an essay published in HME vol XII. In it he declared that once they reached maturity, Dwarves aged little if at all until about the age of 240-

Is it mentioned anywhere when did they reach maturity? I have a conception that those of Durin's folk were mature at the age of 40-50, but I have no clue where has this conception of mine come from and whether it's right or wrong...